CHEMISTRY COMMUNITY

Altamash Mahsud 1I

In that case, oxygen's oxidation number is zero. That is because oxygen is in its natural state. However, if oxygen was in a compound with any other element, it most likely has an oxidation number of -2.

Altamash Mahsud 1I

You cannot tell whether a reaction is endothermic or exothermic just based off of the activation energy. However, if you were given an energy profile, you could tell if it was endo or exothermic.

Altamash Mahsud 1I

k is the rate constant, and is used in the differential rate law. Yes, if k is higher, then the rate of reaction will be higher, meaning the rate will be faster.

Altamash Mahsud 1I

I think you are thinking of the unique rate law, in which the rate of a reaction is with respect to a certain reactant or product. In that case, the stoichiometric coefficient is related to the rate law because you multiply the reciprocal of the stoichiometric coefficient by the reactant/product of ...

Altamash Mahsud 1I

The n in that equation is not the number of moles, but it is instead the number of electrons being transferred in the redox reaction. You can get this number by balancing the redox half reactions and combining these half reactions to get the completed redox reaction, which will tell you the number o...

Altamash Mahsud 1I

A zero-order reaction is one where the rate of reaction does not depend on the concentration of any reactants. In that case, the rate simply equals the rate constant. You can see this through experimental data where the concentration of reactants change, but the rate of reaction does not change at a...

Altamash Mahsud 1I

The unique rate law is when you take the rate of reaction of that reactant (or product), and you divide by the stoichiometric coefficient of that species in the reaction. It should be the same rate for all of the chemical species in the reaction. The differential rate law just takes the concentratio...

Altamash Mahsud 1I

Homogeneous catalysts are in the same phase as the reactants in the reaction that is going to take place. Heterogeneous catalysts are in a different phase than the reactants in the reaction that is going to take place. The significance of this difference is important when you are considering the mec...

Altamash Mahsud 1I

If the order is not told to you in the problem, then there are a few ways of figuring it out. One way could be through experimental data, in which you would see how the rates would change in respect to a reactant concentration changing, then compare the different experiments to find the order with r...

Altamash Mahsud 1I

Termolecular refers to the number of molecules that need to hit each other for a reaction to occur, in this case it is three molecules that need to hit each other in order to react. (this is rare)

Altamash Mahsud 1I

An integrated rate law just shows the concentration of the reactant vs time while the differential rate law shows the rate of reaction vs time.

Altamash Mahsud 1I

If you are referring to kinetics when you say "these reactions", then n is just the order of the reaction. The order of the reaction can give you a basic understanding of how the reaction works (reaction mechanism).

Altamash Mahsud 1I

When asked about k and what can change k, you should know that temperature affects k. This makes sense, because if something were to get hotter, the reaction will go faster (k will increase). The opposite goes for when something gets colder.

Altamash Mahsud 1I

The rate laws in chemistry are instantaneous rates because that rate that you are trying to find is at a specific time t (that is why there is a derivative). You won't need to find the average rate for anything unless specifically asked to do so.

Altamash Mahsud 1I

In an irreversible expansion, the external pressure on something has changed a huge (relative) amount in a short span of time. For an irreversible expansion, the external pressure is constant. For a reversible expansion, the internal and external pressure change in small, infinitesimal increments so...

Altamash Mahsud 1I

Think of it like this: if something is being oxidized, that means it is losing electrons(or electron). Those electrons are going to go to another atom or molecule, which means that atom/molecule that gained those electrons is being reduced. This is why the original atom/molecule that was oxidized is...

Altamash Mahsud 1I

A platinum electrode is used when the reaction that is being studied in the cell does not have a metal that can conduct electricity and transfer the electrons from one side of the cell to the other. You would not need the platinum electrode when you have a reaction taking place that has the metal el...

Altamash Mahsud 1I

It is better to put the oxidation part of the reaction (anode) on the left side and the reduction part of the reaction (cathode) on the right side so you don't confuse yourself because this is how the book does it. The book sets up the cell diagrams in this way too, so it is recommended that you do ...

Altamash Mahsud 1I

A reaction is spontaneous if the delta G is negative, and it is non spontaneous when the delta G is positive. When talking about electrochemistry, a positive E cell means the reaction is spontaneous, and a negative E cell means the reaction is non spontaneous.

Altamash Mahsud 1I

To write a cell diagram, you must keep in mind that for convention (most of the time), the left side of the cell diagram is the anode, and the right side of the cell diagram is the cathode. You write all the solid metals (electrodes) on the outer most parts of both the left side and the right side (...

Altamash Mahsud 1I

Potential difference is simply the amount of energy (work) it takes to move a certain amount of charge some distance.

Altamash Mahsud 1I

Yes it is possible because there could be a metal(solid) on one side of the galvanic cell that actually takes part in the chemical reaction that runs the galvanic cell, so it would be the electrode on that side of the cell. The other side could only have gases or aqueous solutions reacting, so they ...

Altamash Mahsud 1I

Wmax is the same value of delta G at constant temperature and pressure because that is the definition of Gibbs free energy, the amount of energy available to do work, and all of that energy is used for work in an ideal system, which is why the maximum work is done.

Altamash Mahsud 1I

Changing the concentration of the reactants or products will shift the equilibrium of the system. Whether more reactants or products are added or removed, the reaction will shift either to the left or the right. If the reaction shifts to the right, that means more products are being produced, which ...

Altamash Mahsud 1I

If delta G is negative, that means that the forward reaction is favored and that the products will be favored because K>1. (You could then say that the reaction shifts to the right.) If the delta G is positive, that means that the forward reaction is not favored (the backwards reaction is favored) a...

Altamash Mahsud 1I

No, spectator ions are not included in the equilibrium constant because they cross out, because they are on both sides of the chemical equation.

Altamash Mahsud 1I

A closed system cannot exchange matter with its surroundings but it can exchange energy. An isolated system can transfer neither energy nor matter to its surroundings.

Altamash Mahsud 1I

When choosing which Gibbs free energy equation to use, you must know whether or not the system you are looking at is in equilibrium. If the system is in equilibrium, then you use the ∆G°=-RTlnK equation. If not in equilibrium, then you are to use one of the other equations.

Altamash Mahsud 1I

Resonance structures do contribute to the number of microstates a molecule has, but there are other things that contribute as well, such as the vibrational and rotational movements of that molecule.

Altamash Mahsud 1I

The Van't Hoff equation is derived from two Gibb's Free Energy equations that we know of, ∆G°=∆H°-T∆S° and ∆G°=-RTlnK.

Altamash Mahsud 1I

Yes, lone pairs contribute towards the degeneracy of a molecule, as the lone pairs can be oriented in different ways, allowing for more degeneracy for the molecule, increasing it's overall entropy.

Altamash Mahsud 1I

Yes, for the heat of reaction, you must state it in kj/mol because in a reaction, there could be 2 moles of a reactant being used to form a product, and in that case, the per mole part of the heat of reaction matters, because in that case you must divide the amount of heat by two. So yes, the per mo...

Altamash Mahsud 1I

You are correct. For constant volume, since there is no volume change, there is no work being done, so internal energy would just equal heat. (U=q) For constant pressure, there can be both heat transfer and work being done, so then U=q+w. Since in this case there is constant pressure, then heat is j...

Altamash Mahsud 1I

More complex molecules have a higher S because they have a greater amount of rotational and vibrational energies, meaning that they have more possible microstates they can be in, leading to a greater entropy.

Altamash Mahsud 1I

For a gas, when trying to calculate molar entropy, the degenerate states mainly determine the entropy.

Altamash Mahsud 1I

A microstate is simply the one of the different possible arrangements of molecules in a system at any different instant, all with the same energies.

Altamash Mahsud 1I

Substances like O2 and other diatomic molecules, as well as all other elements found in their natural state have an enthalpy of formation of zero because that is how they are found in nature, so there is no amount of heat (enthalpy) needed to form these compounds, because they are already found like...

Altamash Mahsud 1I

The unit for entropy is Joules per Kelvin (J/K).

Altamash Mahsud 1I

For an open beaker system, the beaker is open to the atmosphere, therefore the system and surroundings have the same pressure, in this case, it is the atmospheric pressure.

Altamash Mahsud 1I

A closed system is a system in which matter cannot be transferred between the system and the surroundings, but energy can be transferred between the two. In an isolated system, neither energy or matter can be transferred between the system and the surroundings.

Altamash Mahsud 1I

So the whole concept of Le Chatelier's principle is that you are trying to minimize the effect of some sort of strain you have put on the system. To answer what you're saying, if the concentration of the reactants goes up, then that means you are adding more reactants to the system at equilibrium, s...

Altamash Mahsud 1I

What Hess's law states is that because enthalpy is a state function, enthalpies of reaction can be added together. This means when two or more chemical reactions are added together to get a net reaction, you can get the net enthalpy of reaction by adding the separate enthalpies of reaction of the co...

Altamash Mahsud 1I

Yes, the enthalpy of sublimation can be calculated by adding up the enthalpy of fusion (melting) and the enthalpy of vaporization. This is because enthalpy is a state function, so it can be added up like this, since sublimation is going from a solid directly to a gas, you can just add the enthalpies...

Altamash Mahsud 1I

The temperature of a sample remains constant when undergoing a phase change because all the thermal energy coming from heating up the sample is going into breaking the intermolecular forces between the molecules of that sample. Since all of the energy is going into breaking those IMF's, then the ene...

Altamash Mahsud 1I

The reason why steam burns worse than water is because steam must undergo a phase change, it must condense when coming in contact with skin. The amount of energy released into your skin from this phase change is very high, it is the enthalpy of condensation (equal but opposite sign of the enthalpy o...

Altamash Mahsud 1I

When first learning about the concept that water molecules interact with each other and a small percentage of them form H3O+ and OH-, I was taught that it was called the autoionization of water. In lecture, it said the autoprotolysis of water, what is the difference between the two terms in this case?

Altamash Mahsud 1I

Depending on the units they provide to you in the problem, you will use either Kc or Kp. For example, if they were to give you the partial pressure of reactants that were in the gas phase, say in the unit bar, then you would use Kp. But if they were to give you the molar concentrations of those reac...

Altamash Mahsud 1I

Many solvents other than water have the ability of autoprotolysis, and they have their own values of Kw as well, though it would not be called Kw because Kw is only for water.

Altamash Mahsud 1I

Le Chatlier's principle states how if you apply stress to a chemical reaction in equilibrium (changes in pressure, temperature, volume, concentrations of reactants/products), then the equilibrium of that chemical reaction will shift either to the left or right, in order to oppose the stress placed o...

Altamash Mahsud 1I

Hey Kevin, when given these types of questions and trying to understand a concept, in this case Le Chatlier's principle, then if the amount of a reactant is not stated in the problem you can assume that it is in excess. Have a good day :)

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