# Questions tagged [enthalpy]

A thermodynamic state function describing the total energy content of a system.

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### Enthalpy change defined at constant pressure only?

Is change in enthalpy defined only at constant pressure? I know Q-W=del(U) And Q at constant pressure equals del(H) (enthalpy change). Can Q (heat given to the system) be used interchangeably ...
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### Enthalpy and Internal Energy in Constant Volume Calorimeter

It is my understanding that enthalpy differs from internal energy only in that the change in enthalpy takes into account any pressure-volume work done on the system (or by the system) in a reaction, ...
3answers
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### Intuition on Gibbs Free Energy

In many places, I read that Gibbs Free Energy is called "free energy" because some of the enthalpy that comes from the chemical reaction becomes "waste heat" due to a change in the entropy of the ...
1answer
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### Finding the energy given out when 2 moles of reactants are mixed and ignited from a balanced equation

The question I am trying to answer is this: I only know about Hess' law, bond enthalpies and enthalpies of combustion and have tried to use all concepts in order to somehow get an answer but none of ...
0answers
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### Entropy and enthalpy of hydrogen ion?

The absolute entropy of $\ce{H^+ (g)}$ is $\ce{108 kJ/mol.K}$. However, the absolute entropy of $\ce{H^+ (aq)}$ is exactly 0. Why is that? Also, the standard enthalpy of $\ce{H^+ (aq)}$ is 0, so ...
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1answer
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### Relation between enthalpy and Cv

MY ATTEMPT We already know that $\Delta U=nC_V\,\Delta T$ which is for constant volume Now we know that $\Delta H = \Delta U + p\,\Delta V$ so $\Delta H = nC_V\,\Delta T + 0$ (as at constant volume ...
1answer
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### Difference between thermodynamic terms heat and enthalphy [closed]

What is the difference between heat and enthalphy?
1answer
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### Joules to kJ/mol conversion

In my AP Chem class we are working on testing Hess's Law and conducted three reactions. Then enthalpy changes of the 1) $\ce{NaOH + HCl}$ and 2) $\ce{NaOH + NH4Cl}$ to predict the enthalpy change of 3)...
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1answer
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### heat of fusion in an equation

You add $100.0\ \mathrm g$ of water at $55.0\ \mathrm{^\circ C}$ to $100.0\ \mathrm g$ of ice at $0.00\ \mathrm{^\circ C}$. Some of the ice melts and cools the water to $0.00\ \mathrm{^\circ C}$. ...
2answers
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