# Questions tagged [enthalpy]

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

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### Difference between exothermic and exergonic

In High School I learned that an exothermic reactions releases energy, while an endothermic reaction needs energy to occur. Now I learned that there is a separate, somewhat similar classification ...
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### Why is heating increasing the solubility of sodium hydroxide?

\begin{align} \ce{NaOH &-> Na+ + OH-} & \Delta H^\circ &= \pu{-44.51 kJ/mol} \end{align} The dissolution of sodium hydroxide in water is an exothermic process, and so, according to Le ...
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### C-C bond dissociation energy

Have the various $\ce{C-C}$ bonds in straight chain hydrocarbons, have the same dissociation energies? Or does it depend on the location of the carbon in the chain? In other words, are the terminal ...
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### How to calculate the mass of iron with a temperature of 325 °C needed to melt ice and raise the temperature of water from 0 to 22 °C?

A large well-insulated container holds a mixture of $75\ \mathrm g$ of ice and $100\ \mathrm g$ of water at $0\ \mathrm{^\circ C}$. Using the data given below, calculate the mass in grams of solid ...
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### What is an example of a very low temperature endothermic reaction?

Shakashiri describes the reaction of solid Ammonium Thiocyanate and solid Barium Hydroxide Octahydrate resulting in an endothermic reaction leading to subzero temperatures. I've performed this ...
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### Algebra of conserved quantities for chemical reactions

So there is the standard formation enthalpy $\Delta H^0_f$ and there is also formation entropy. Are there more (independent) quantities? What about the heat capacity? Is there a general theoretical ...
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### Heats of formation of neutral molecules and homolytic vs heterolytic bond dissociation in mass spectrometry

I am currently studying the textbook Mass Spectrometry, third edition, by Jürgen H. Gross. Chapter 2.4.3 Bond Dissociation Energies and Heats of Formation says the following: Great efforts have been ...
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### Is the standard enthalpy of formation always non-positive?

If the standard enthalpy of formation is defined as the energy change when 1 mole of a substance is formed from its elements in their standard states and forming chemical bonds is an exothermic ...
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### How to calculate the entropy change of benzene when it changes from vapour into liquid?

Given information: The boiling point of benzene at atmospheric pressure is $353~\mathrm{K}$ the enthalpy of vaporization of benzene is $30.8~\mathrm{kJ~mol^{−1}}$ at this temperature. ...
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### Enthalpy definitions. What are their main differences?

The definition of enthalpy is properly described in here. The principal objective of this question is mainly academic. In order to any students with internet connection can find a definition and an ...
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### Why is the standard enthalpy of formation of elements in their native forms zero?

Why is the standard enthalpy of formation of $\ce{O2}$ and other reference forms of elements equal to zero? Well, from what I know, bonding releases energy. Also, does anybody know a source for ...
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### What is the bond energy of H-O? Wikipedia disagrees with itself

What is the bond energy of H-O? Wikipedia disagrees with itself: On English Wikipedia: 467 kJ/mol On French Wikipedia: 366 kJ/mol What is the right value?
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### Infinite Increase in Entropy when Energy added to Absolute Zero

My textbook states the following: If a system were at absolute zero, an additional small amount of heat energy would lead to an infinite increase in entropy. Such a state is impossible. Absolute ...
Question 28 from [1, p. 4.4]: An ideal gas is expanded irreversibly from $\pu{5 L}$ to $\pu{10 L}$ against a constant external pressure of $\pu{1 bar}.$ The value of heat involved $(q)$ in this ...