Endothermic v. Exothermic
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Endothermic v. Exothermic
In class today, we learned about endothermic reactions in depth (vaporization, fusion, sublimation) and that the have a positive delta H. Will they ALWAYS have a positive delta H? Does that mean that exothermic reactions will ALWAYS have a negative delta H?
Are there any exceptions to this rule?
Are there any exceptions to this rule?
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Re: Endothermic v. Exothermic
I assume that's the case, since the sign of delta H is kind of "built in" to the definitions of endothermic and exothermic. Negative delta H means heat is released, so it's exothermic, while positive means heat is absorbed which is endothermic.
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Re: Endothermic v. Exothermic
Yes, endothermic reactions will always have a positive delta H, and exothermic reactions will always have a negative delta H.
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Re: Endothermic v. Exothermic
I think that endothermic reactions will always have a positive change in enthalpy because in order for the reaction to be classified as endothermic in the first place, heat must be absorbed.
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Re: Endothermic v. Exothermic
Yes. Endothermic reactions will always have a positive Delta H as they are absorbing energy so the products will have more energy than the reactants. Same with exothermic reactions, Delta H will always be negative because the products will have less energy than the reactants.
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Re: Endothermic v. Exothermic
Whether heat is absorbed or released determines if the reaction is endothermic or exothermic. A reaction that absorbs heat will be endothermic with a positive delta H.
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Re: Endothermic v. Exothermic
Yes, I believe the value of delta H (positive or negative) is the determining factor of whether something is endothermic or exothermic. In an endothermic reaction, heat is required, so delta H will always be positive. In an exothermic reaction, heat is released, so delta H will always be negative.
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Re: Endothermic v. Exothermic
Hi! Yes, endothermic reactions will always have a positive enthalpy indicating the absorption of heat whereas exothermic reactions will always have a negative enthalpy indicating the release of heat. Hope this helps! :)
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Re: Endothermic v. Exothermic
I do not believe that there are any exceptions to the rule, and you are correct. This is due to the nature of "delta H" itself. Delta H is the change in enthalpy. So, when you have a positive value, it tells us that the enthalpy in the products is higher than the reactants, which mean it requires energy or heat to get it to change. With this, the opposite is true for exothermic reactions, or negative delta H values.
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Re: Endothermic v. Exothermic
Yes, I think those statements should always be true. You can tell if a reaction is exothermic or endothermic by calculating its delta H. If it is positive, the reaction is endothermic, and if it is negative, the reaction is exothermic. This statement would make sense because H is enthalpy which is the amount of heat released or absorbed, which is basically also showing whether the reaction is exothermic or endothermic in the process.
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Re: Endothermic v. Exothermic
Just a side note: fusion, vaporization, and sublimation aren't really reactions because there aren't any chemical bonds being broken, they're considered phase changes and are physical changes because it's just the intermolecular attractions that are being overcome.
Re: Endothermic v. Exothermic
Endothermic reactions will have a positive delta H because the reaction requires heat. In contrast, exothermic reactions will have a negative delta H because the reaction gives a net release of heat.
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Re: Endothermic v. Exothermic
I do not believe there are any exceptions to this rule. Exothermic means releasing heat, so a positive delta H would not be possible. The vice versa applies to endothermic, which takes in heat, so a negative delta H would not be possible.
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Re: Endothermic v. Exothermic
I believe so; endothermic reactions will always have a positive enthalpy and exothermic reactions will always have a negative enthalpy.
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Re: Endothermic v. Exothermic
Endothermic reactions always have a +ve delta H, while exothermic reactions always have a -ve delta H.
I don't believe that there are any exceptions to this rule.
I don't believe that there are any exceptions to this rule.
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Re: Endothermic v. Exothermic
Yes if you are losing heat from the system,endothermic, the delta h will be negative
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Re: Endothermic v. Exothermic
An endothermic process has a positive delta H because the system is gaining heat. An exothermic process has a negative delta H because the system is losing heat.
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Re: Endothermic v. Exothermic
That's right, since exothermic reactions will be losing heat, that means that the delta h must be negative.
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Re: Endothermic v. Exothermic
yea, endothermic rxns will always have a positive delta H, and exothermic rxns will always have a negative delta H
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Re: Endothermic v. Exothermic
Yes, that is correct! Exothermic reactions always have a negative delta H, and an endothermic reaction will always have a positive delta H.
Hope it helps!
Hope it helps!
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Re: Endothermic v. Exothermic
Yes exothermic will always have a delta - H and endothermic will always have a positive delta H as that is the definition. negative delta H means that the system is releasing energy and positive delta H means
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Re: Endothermic v. Exothermic
Endothermic reactions always have net positive delta H and exothermic reations always have net negative delta H, but for differing reactions you could have different "paths". For example if you burn glucose in the lab there is one exothermic step, but in the body there are many, with some exothermic and some endothermic(energy investment) steps. But enthalpy is a state property, meaning both reactions have overall net negative delta H and they are both considered to be favorable or exothermic.
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Re: Endothermic v. Exothermic
Yes, I would say so in my opinion but I don't know if there any exceptions out there. To be clear, sublimation, vaporization, and fusion all are endothermic to begin with and you have to add heat to the system for there to be a phase change from ice to steam, that is why they all have positive delta H values. Since the change in enthalpy basically corresponds to the absorption of heat by a system, and exothermic reactions release heat, there has to be a negative delta H value.
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Re: Endothermic v. Exothermic
Yes, a negative delta H is always going to be exothermic because it released heat in the process, making enthalpy a negative value. Additionally, a positive delta H value will always be endothermic because it required heat in the process!
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Re: Endothermic v. Exothermic
Yes, because a positive delta H is absorbing heat and a negative delta H is releasing heat.
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Re: Endothermic v. Exothermic
Exothermic reactions will always be negative because the total energy of the products is less than that of the reactants which is why energy gets released.
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Re: Endothermic v. Exothermic
Endothermic reactions will always have a +H and exothermic reactions will have a -H. if heat is showed in the reaction on the reactants side it is endothermic and if it is present on the products side it is an exothermic reaction.
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Re: Endothermic v. Exothermic
Yes, endothermic reactions will always have a positive delta H (meaning that it absorbs energy), and exothermic reactions will always have a negative delta H (as it releases energy).
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Re: Endothermic v. Exothermic
Yes! Endothermic reactions will always have a positive enthalpy change and exothermic reactions will always have a negative enthalpy change.
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Re: Endothermic v. Exothermic
Yes, endothermic reactions have a positive delta H since they require energy while exothermic reactions have a negative delta H since they release energy.
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Re: Endothermic v. Exothermic
I think at least according to the definition, endothermic reaction has positive H while exothermic reaction has negative H.
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Re: Endothermic v. Exothermic
I think so, if the sign changes, their property would change too, so endothermic reaction would be exothermic
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Re: Endothermic v. Exothermic
I believe you're right! When the enthalpy is positive, we can think of the endothermic reaction as heat going into the system, so the increase in heat is represented with +. When the enthalpy is negative, the endothermic reaction releases--or loses-- heat, so the decrease in heat in the overall system is -.
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Re: Endothermic v. Exothermic
An endothermic reaction will always have a positive delta H because, for a reaction to endothermic, it absorbs heat. An exothermic reaction will always be a negative delta H because, for a reaction to be exothermic, it gives off heat.
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Re: Endothermic v. Exothermic
Yes, this is definitely true. Exothermic reactions are always labeled by a negative delta H, whereas endothermic reactions are always labeled by a positive delta H. This is due to how exothermic reactions release heat, whereas endothermic reactions absorb heat.
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Re: Endothermic v. Exothermic
Yes, endothermic reactions absorb heat hence the negative delta H. Exothermic reactions release heat hence the positive delta H.
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Re: Endothermic v. Exothermic
Definitely, use the delta H to determine whether is endothermic or exothermic.
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Re: Endothermic v. Exothermic
Delta H represents the change in enthalpy, which is the total heat content of a system. So yes, the positive or negative sign of delta H should be used to determine whether a reaction is endothermic or exothermic. When it is less than zero, this means that heat has been released from the system, indicating an exothermic reaction. Similarly, when it is greater than zero, heat has been absorbed, indicating an endothermic reaction.
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Re: Endothermic v. Exothermic
Yes. You can also make sense of this by thinking about enthalpy being a state property. As long as the amount of heat is greater than the system began with, it is definitely endothermic, and vice versa for exothermic reactions.
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Re: Endothermic v. Exothermic
I don't think there are any exceptions to this rule! Exothermic reactions will have a negative delta H and endothermic reactions will have a positive delta H.
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Re: Endothermic v. Exothermic
that is correct, endothermic reactions will always have positive delta H values because they absorb heat and exothermic reactions will always have negative delta H values because they release heat.
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Re: Endothermic v. Exothermic
I do think that these are always true because the definition of endothermic is that it requires heat (and exothermic releases heat). This probably means that endothermic reactions will always have a positive delta H and exothermic reactions will always have a negative delta H. I'm not sure if there are any exceptions, but I don't think we will need to know that for this class.
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Re: Endothermic v. Exothermic
Yes, by definition an endothermic reaction requires heat (positive H) whereas an exothermic reaction expels heat (negative H
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Re: Endothermic v. Exothermic
Yes, endothermic reactions will always have a positive delta H because the change is positive and exothermic reactions will always have a negative delta H because the change is negative.
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Re: Endothermic v. Exothermic
Yes that is right. I don't think there are any exceptions that can bend the rule for it but I'm pretty positive that's the case
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Re: Endothermic v. Exothermic
Endothermic reactions have a positive delta H and exothermic reactions have a negative delta H.
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Re: Endothermic v. Exothermic
Yes! Endothermic reactions will always have a positive delta H as the system absorbs energy while exothermic reactions release energy from the system, resulting in a negative delta H
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Re: Endothermic v. Exothermic
yes!! endothermic reactions will always have a positive delta H and exothermic reactions will always have a negative delta H
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Re: Endothermic v. Exothermic
Yep, endothermic reactions will always have a positive delta H, because this type of reaction takes in heat, thus it would have a positive change in enthalpy. On the other hand, exothermic reactions will have a negative delta H because you lose heat while the reaction is taking place, thus resulting in a negative change in enthalpy.
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Re: Endothermic v. Exothermic
Yes! Any endothermic reaction would have a positive ∆H value and any exothermic reaction would have a negative ∆H value.
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Re: Endothermic v. Exothermic
Exothermic reactions have a negative delta H and endothermic reactions have a positive delta H.
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Re: Endothermic v. Exothermic
Yes, endothermic reactions will always have a positive delta H because it indicates that the reaction is taking in heat, while exothermic reactions will always have a negative delta H because that indicates that the reaction is giving off heat.
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Re: Endothermic v. Exothermic
you can think of an endothermic reaction as the system you're viewing "gaining" enthalpy or heat. This would mean that your △H is positive.
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Re: Endothermic v. Exothermic
Yes, like others have said, endothermic reactions will always have a positive delta H and exothermic reactions will always have a negative delta H
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Re: Endothermic v. Exothermic
Endothermic reactions will always have a positive delta H whereas an exothermic reaction will always have a negative delta H.
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Re: Endothermic v. Exothermic
Yeah exothermic reactions also have a negative delta H and endothermic reactions always have a positive delta H because of the way exothermic reactions are defined as releasing energy while endothermic reactions are defined as absorbing energy.
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Re: Endothermic v. Exothermic
Exothermic reactions have a negative delta H and endothermic reactions have a positive delta H
Re: Endothermic v. Exothermic
Endothermic will always be a positive enthalpy value and exothermic will always be a negative enthalpy value.
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Re: Endothermic v. Exothermic
Yes endothermic reactions are always positive and exothermic reactions are always negative.
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Re: Endothermic v. Exothermic
Yes, I believe this is always the case. Endothermic reactions have a positive delta H, and exothermic reactions have a negative delta H. Vaporization and fusion are always endothermic (because you need to put in heat to get liquids to their gas state and solids to their liquid state), and condensation of gas into liquid and liquid to solid is exothermic.
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Re: Endothermic v. Exothermic
Yes, this is true. Endothermic reactions will always have a + delta H, and exothermic reactions will always have a - delta H, this is the case for all
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Re: Endothermic v. Exothermic
Lorena_Morales_1K wrote:Why is bond formation exothermic again?
I believe it's exothermic because the system loses energy to form the bonds and since there's a decrease in energy, the energy is lost as heat and makes the process exothermic
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Re: Endothermic v. Exothermic
The definition of delta H is the change in enthalpy of a system. The definition of exothermic is that heat is released during a reaction and the enthalpy of the system decreases (which can only ever be represented by a negative delta H). The opposite is true of endothermic. So, you are right and there are no exceptions.
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Re: Endothermic v. Exothermic
Lorena_Morales_1K wrote:Why is bond formation exothermic again?
Bonded atoms/molecules are more stable. Unbound atoms require energy to keep them apart which is released when they form a bond, making bond formation exothermic.
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Re: Endothermic v. Exothermic
Yes, endothermic will be positive since it is absorbing heat and exothermic will be negative since it is releasing heat.
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Re: Endothermic v. Exothermic
Yes that will always be the case! I have not heard Lavelle or anybody else speak to any exceptions to the rule!
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Re: Endothermic v. Exothermic
Endothermic reactions will always have a positive deltaH because they require energy. On the other hand, exothermic reactions will always have a negative deltaH because they release energy.
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Re: Endothermic v. Exothermic
Exothermic reactions will always be negative because the total energy of the products is less than that of the reactants which is why energy gets released.
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Re: Endothermic v. Exothermic
Endothermic reactions will always be positive and exothermic reactions will always be negative.
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Re: Endothermic v. Exothermic
Endothermic reactions will always be positive because they require heat to occur, and exothermic reactions will always be negative because they release heat and therefore lose energy.
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Re: Endothermic v. Exothermic
Yes endothermic reactions will always have a positive enthalpy and exothermic reactions will always have a negative enthalpy/delta H
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Re: Endothermic v. Exothermic
Yep, endothermic will always be positive, since an endothermic reaction always takes in energy, while exothermic will always be releasing, and therefore always negative :))
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Re: Endothermic v. Exothermic
Yes, you'll find that exothermic reactions will always have a negative delta H while endothermic reactions will always have a positive delta H. This is due to the fact that heat is either being released or absorbed.
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Re: Endothermic v. Exothermic
yes, I think it is common that positive H is always endothermic and exothermic is always negative. There is no real expectation of these rules because H will always change based on the environment and changes.
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Re: Endothermic v. Exothermic
Endothermic reactions are characterized by their positive "delta H" values. In endothermic reactions, temperature/heat can be treated as a "reactant." Thus, when temperature is increased, the reaction will shift to the right, and when temperature is decreased, the reaction will shift to the left.
Exothermic reactions are characterized by their negative "delta H" values. In exothermic reactions, temperature/heat can be treated as a "product." Thus, when temperature is increased, the reaction will shift to the left, and when temperature is decreased, the reaction will shift to the right.
Exothermic reactions are characterized by their negative "delta H" values. In exothermic reactions, temperature/heat can be treated as a "product." Thus, when temperature is increased, the reaction will shift to the left, and when temperature is decreased, the reaction will shift to the right.
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Re: Endothermic v. Exothermic
I am pretty sure because of the nature of exothermic and endothermic reactions, exothermic will always be negative and endothermic will always be positive. Exothermic is releasing heat, so the object or substance of interest would be losing heat, with a -delta H. Endothermic is requiring heat, so the object or substance of interest would be gaining heart, with a +delta H.
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Re: Endothermic v. Exothermic
Yes, endothermic reactions will always have a positive delta H, and yes, exothermic reactions will always have a negative delta H. There are no exceptions to this rule.
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Re: Endothermic v. Exothermic
Delta H is positive when the reaction is endothermic because heat is absorbed while delta H is negative when the reaction is exothermic because heat is released.
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Re: Endothermic v. Exothermic
Endothermic reactions have a positive delta H because the system is absorbing heat from the surroundings. Exothermic reactions have negative delta H because the system is releasing heat into the surroundings.
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Re: Endothermic v. Exothermic
Yes, endothermic reactions always have positive delta H values while exothermic reactions will always have a negative delta H value.
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Re: Endothermic v. Exothermic
I'm pretty sure that there will be no exceptions to the fact that delta H is positive and negative for endothermic and exothermic reactions, respectively. Other things to keep in mind when differentiation between the two include:
Endothermic
- energy absorbed
- bonds broken
- strong reactant bonds
Exothermic
- energy released
- bonds formed
- strong product bonds
Endothermic
- energy absorbed
- bonds broken
- strong reactant bonds
Exothermic
- energy released
- bonds formed
- strong product bonds
Re: Endothermic v. Exothermic
Endothermic reactions has a positive delta H value while exothermic has negative.
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Re: Endothermic v. Exothermic
Exothermic reactions will always have negative delta H because heat is being released, which is denoted with a negative sign. Endothermic reactions will always have positive delta H because heat is being absorbed, which is denoted with a plus sign.
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Re: Endothermic v. Exothermic
Yes, you're correct. Exothermic reactions will always have a negative delta H, while endothermic reactions will always have a positive delta H. Endothermic reactions take up energy, making their delta H positive while exothermic reactions give away energy to its surroundings, making their delta H negative.
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Re: Endothermic v. Exothermic
Exothermic reactions are a release in heat and, thus, they have a negative value associated with them. An absorption in energy/heat is an endothermic process, and, therefore, it will always be positive.
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Re: Endothermic v. Exothermic
Endothermic reactions will always have a positive delta H, because they are taking in heat/energy. Exothermic reactions will always have a negative delta H, because they are releasing heat/energy.
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Re: Endothermic v. Exothermic
Yes, by definition, I believe positive delta H is endothermic because it's a gain in energy, meaning a positive delta H.
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Re: Endothermic v. Exothermic
That will always be the case as when you have to input energy, delta H has to be positive
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Re: Endothermic v. Exothermic
Yes exothermic reaction always have a negative delta H and endothermic reactions have a positive delta H
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Re: Endothermic v. Exothermic
Regarding phases change, when a solid becomes to liquid, heat is NEEDED to melt the solid.. also known as endothermic
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Re: Endothermic v. Exothermic
Endothermic means energy went into the system which means delta H increased so it has to be positive. And the opposite is also true.
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Re: Endothermic v. Exothermic
Yes they will always act this way; exothermic reactions will always be losing heat, meaning that the delta h must be negative and endothermic reactions will always be gaining heat with a positive delta h
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Re: Endothermic v. Exothermic
Yes, exothermic reactions will always have a negative H. However, if the Recants acclimate then it can become spontaneous which I don't know if that shows more about h or the G.
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