# Questions tagged [enthalpy]

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

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### How to determine Delta H from the heat of combustion?

The heat of combustion of 2-propanol at 298.15 K, determined in a bomb calorimeter, is -33.41 kJ/g. For the combustion of one mole of 2-propanol, determine (a) $\Delta U$ and (b) $\Delta H$ So I ...
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### Why is the enthalpy change not zero in an adiabatic process?

Which of the following must be true for adiabatic processes? $C_V = C_p$ $\Delta H = 0$ $\Delta U = 0$ $\Delta S = 0$ $q = 0$ (Source: Chemistry GRE) The answer is $q = 0$. From ...
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### Intuition for electrode potential

If I connect a zinc half cell (Left hand side) and a copper half cell (right hand side), I get an E cell value of 1.1V taken from the voltmeter. If I replace the voltmeter with a light bulb, I will ...
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### Does the bond dissociation enthalpy vary with temperature?

The $\ce{H-H}$ bond enthalpy is $436 \mathrm{kJ/mol}$: $$\ce{H2 (g) -> 2H (g)} \qquad \Delta H = +436 \mathrm{kJ/mol}$$ Does this only apply at the standard temperature of $298 \text{K}$, i.e. ...
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### Mathematical basis of why enthalpy of mixing is 0 for ideal gas

For this case, let's say there are two identical chambers connected by a small tube, constant pressure and temperature. There's a closed valve that separates the two chambers. Within the chambers ...
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### Enthalpy: when and how does it vary? [closed]

I have been looking for a physical explanation for entropy and enthalpy variations. An example would be the air system of a vehicle, where people say we have a strong enthalpy and entropy variations ...
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### Calculating standard enthalpy of reaction, which reactant to choose for the amount of substance

For example, this reaction: $$\ce{2NaOH + H2SO4 -> Na2SO4 + H2O}$$ Suppose both concentrations are $1\ \mathrm{mol\ l^{-1}}$ (standard condition). There is $0.02\ \mathrm{mol}$ ($20\ \mathrm{cm^3}$...
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### What non-toxic non-water substances have a freezing point very close to water's?

I was linked to a Kickstarter for a cooling ball to be placed in drinks which claims with constant marketing hyperbole how much it relies on "Phase Change" ! which is a neat concept and seems not ...
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### What is the standard heat of formation of the nitrate ion, based on the standard enthalpy of formation of silver nitrate?

Given the standard enthalpy of formation of $\ce{AgNO3(aq)} = -99 \text{ kJ/mol}$ and the standard enthalpy of formation of $\ce{Ag+(aq)} = +105 \text{ kJ/mol}$, what's the standard heat of formation ...
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### When is it okay to use $Q=mc\Delta T$, is this equation only for calorimetry questions?

When is it okay to use $Q=mc\Delta T$, is the equation only for calorimetry questions? When a question talks about heat how do I know if i'm measuring $\Delta H$ or Q?
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### What defines the specific enthalpy of atomization? [duplicate]

1 mol of $\ce{F2}$ is turned into $\ce{2F}$ (atoms). Is this the specific enthalpy of atomization, or two times that?
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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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### Enthalpy Calculations, Heat of Formation/Combustion

I just don't understand how to do these and would really appreciate your help. 1) Ammonium dichromate decomposes in a reaction when heated. Calculate the heat transferred for the decomposition of 53....
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### How can oxygen atoms suddenly appear on the product side of an equation?

The question states the following equation: $$\ce{C(s) + 2H2(g) -> CO2(g) + 2H2O}$$ And then asks you to calculate the enthalpy change for it, given enthalpies of combustion. The stated values ...