Enthalpy

[Marnie Cavanaugh- 1A]

I was wondering if someone could explain the relationship between enthalpy and the terms exothermic/ endothermic. Are these two terms used to describe specific enthalpy reactions? Or?

[jhb123]

Hello!

Enthalpy is the amount of heat released/absorbed at constant pressure.

In exothermic reactions, enthalpy (represented by delta(H)) is negative. Heat is released and, as a result, the surroundings are warm.
In endothermic reactions, enthalpy is positive. Heat is required and, as a result, the surroundings are cool.

In exothermic reactions, enthalpy of the reactants (initial) is greater than that of the products (final).
In endothermic reactions, enthalpy of the reactants (initial) is less than that of the products (final).

Hope this helps :)

[Michelle Fong 3F]

Enthalpy, ΔH, refers to how much heat is absorbed or released by a reaction occurring at a constant pressure. It can be written as the difference between the enthalpies of the reactants and products. A reaction that creates a net release of energy is said to be exothermic and ΔH would be negative. A reaction that requires a net input of energy is said to be endothermic and ΔH would be positive.

[Mia Donato]

Hello! Enthalpy is the amount of heat released or absorbed at constant pressure. deltaH is the change in enthalpy. If the chemical reaction gives a net release of heat, deltaH (Hproducts -Hreactants) will be negative, which means the reaction is exothermic. Similarly, if the chemical reaction requires heat, deltaH will be positive, which means the reaction is endothermic.

[Madeline Redmond 2A]

Since enthalpy is the amount of heat released or absorbed at a constant pressure, the reaction is exothermic or endothermic depending on if the heat is released or absorbed. When heat is released, the deltaH value is negative, so the reaction is exothermic, making the surroundings warm. But when heat is absorbed, the deltaH value is positive, so the reaction is endothermic, making the surroundings cool.

[Litsa Dimit 1D]

A reaction is exothermic and will have a negative enthalpy if it releases more energy than it takes in. Consider the exothermic as having been "subtracted" from the reaction. A reaction is endothermic, and its enthalpy will be positive if it absorbs or utilizes more energy than it generates.

[Caitlin Beale 3E]

Enthalpy is deifined as the amount of heat released or absorbed at a constant pressure. If heat is released during a reaction, it is exothermic and delta H is negative. If heat is absorbed during a reaction, it is endothermic and delta H is positive.

[Daniella Viorato 2G]

hey marnie, just a small tip if you're ever confused on which is which -
- EXothermic --> heat is released (heat is EXiting the system)/bond breaks/negative deltaH value
- endOthermic --> heat is absorbed (i like to think of heat being absorbed by the big O in endOthermic)/bond forms/positive deltaH value
hope this helps in any way! :)

[Nala Son 3B]

Hi!
Enthalpy refers to energy being released or absorbed and is represented by delta H. In an endothermic reaction, energy is being absorbed/utilized, meaning that enthalpy (delta H) will be positive as it is taking energy into the system. In an exothermic reaction, energy is being released, meaning that enthalpy (delta H) will be negative as it is releasing energy out of the system.

[Freddie P-G 1H]

exothermic reactions release energy to make new bonds, whereas endothermic reactions put in energy to break bonds. Energy is required to break bonds, so endothermic reactions take in heat : delta h is positive. Exothermic reactions release heat so delta h is negative.

[Brianna Bui 2J]

Hi!

Enthalpy is commonly referred to as heat, but is also the energy stored in potential bonds. Change in enthalpy is written as delta H.

Exothermic reactions result in a release in heat, so delta H is negative. Heat is released to the surroundings. Forming bonds results in a release of energy and is thus an exothermic reaction. In a chemical equation, exothermic reactions could be written with heat on the side of the products.

Endothermic reactions result in an absorption of energy from the surroundings, so delta H is positive. Breaking bonds requires energy and is thus an endothermic reaction. In a chemical equation, endothermic reactions could be written with heat on the side of the reactants.

[Lizze Cardoso 2I]

Hi! Enthalpy is a state property that explains how much heat is released or absorbed at a constant pressure. If the change in enthalpy is negative, the reaction is exothermic because it releases heat. However, if the change in enthalpy is positive, the reaction is endothermic because heat is required.

[Yasmin Moosavy1A]

Enthalpy is heat released or absorbed in a reaction. So basically, explaining what happens to the energy of system when a reaction occurs. Does outside energy have to be inputed to drive the reaction or is it a reaction that releases energy which could possibly drive other reactions with its energy. A positive H means it needs energy (so it is absorbed) which is by definition what an endothermic reaction is. And vice versa for exothermic. This also comes in with biological systems where there are coupled reactions, so the energy of one drives another.

[Maya_Panozzo_2D]

In the lecture at the beginning of class, Lavalle gave the definition of enthalpy as "the study of heat released or absorbed in chemical reactions and physical changes" but later in the lecture, he also gave the definition that enthalpy is the "amount of heat released or absorbed at a constant pressure". I'm just not sure which is correct or if they both are.

[Devin Ma 3A]

Enthalpy can refer to how much of heat is released or absorbed at a constant pressure, and may also refer to whether a reaction will require energy to break bonds or release energy to form bonds. A negative enthalpy indicates an exothermic reaction because it releases energy, therefore, can form bonds. On the other hand, a positive enthalpy indicates an endothermic reaction because it requires energy, therefore, can break bonds. A reaction must have an enthalpy, which is either positive or negative, because a reaction must either be endothermic or exothermic.