# Questions tagged [enthalpy]

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

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### What is the unit of enthalpy? [closed]

I have seen both kJ and kJ/mol as units for enthalpy and enthalpy of formation and enthalpy of combustion in my book, can both be used? And also what is the unit of Gibbs free energy, kJ or kJ/mol? ...
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### Atomization enthalpy trends. The case of Phosphorus

I was looking again at the periodic trends like Ionization Energy, Electron Affinity, Radius and so on. I understood all the general trends and the exeptions for these ones, but I can't fully ...
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### How should I evaluate $\left(\frac{\partial U}{\partial V}\right)_T$ with van der waals equation: $P = \frac{nRT}{V-nb}-a(\frac{n}{V})^2$?

So in my homework I was able to get this- $\left(\frac{\partial U}{\partial V}\right)_T = T(\frac{\partial P}{\partial T})_V - P$ but now I'm trying to plug in $P = \frac{nRT}{V-nb}-a(\frac{n}{V})^2$ ...
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### Calculating Enthalpy Change from Calorimetry [closed]

What calculating the enthalpy change of a reaction, for example 5g of CaCl2 dissolving in 100 mL of water, is m the mass of water or the mass of water plus the mass of the salt. q = (105g)(4.18)T or q ...
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### How does the enthalpy change of bond enthalpy relate to enthalpy changes of formation? What's the difference? [duplicate]

The enthalpy change = sum of bond energies broken (reactants) - sum of bond energies made (products). Then I read The enthalpy change = sum of the enthalpy change of formation of products - sum of the ...
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### In acids why does polarising the O-H bond weaken rather than strengthen it?

In hexaaquaions it is generally true that aqueous solutions of complex ions with a higher positive charge on the central metal ion will have a lower pH. Explanations typically note that the greater ...
28 views

### Which is chemical reaction has the highest energy density? [duplicate]

Lets say X and Y react to form XY, and release E Joules of energy in total, not per mole. If molar weight of X is 1 g and Y is 2 g So the energy density is 1000E/3 J/Kg. Which chemical reaction has ...
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### Why is octasulfur present in equation for standard enthalpy of formation of sulfuric acid?

Write a balanced chemical equation corresponding to the standard enthalpy of formation of $\ce{H2SO4}.$ \eqref{rxn:r1} is the given answer, \eqref{rxn:r2} is my answer: \begin{align} \ce{1/8 S8 (s) + ...
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### What do they mean with temperature in the formula for enthalpy?

I'm studying enthalpy and I'm having a real hard time trying to conceptualize it. I can do the exercises and know the formulas but I feel like I lack an understanding of what it actually is. One of my ...
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### What is the most stable cycloalkene? [closed]

I'm looking specifically at cyclopentene and cyclohexene. Supposedly, greater instability would lead to a more exothermic enthalpy of combustion. However, based on my data, cyclopentene is more ...
1 vote
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### Enthalpy Departure

I'm trying to fill in the steps from my textbook on the derivation of enthalpy departure from ideal gas behavior. My textbook gives the variation of mass-specific enthalpy with temperature pressure as ...
1 vote
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### What is the difference between ΔH = ΔU +Δ(PV) and ΔU = q + w? [closed]

Here, ΔH = Enthalpy change, ΔU = Change in internal energy, P = pressure and V = volume. I know that ΔH(Enthalpy) is heat given/taken to/from system at constant pressure. But I have been practicing ...
185 views

### Enthalpy in the van't Hoff equation

In the van't Hoff equation, why do we say that the change in enthalpy at standard pressure is constant? My book derives the equation for a mixture of ideal gases reacting with each other. The proof ...
1 vote
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### Relation between enthalpy and internal energy for chemical reaction at constant volume

Question The combustion of benzene(l) gives $\ce{CO2(g)}$ and $\ce{H2O(l)}.$ Given that the heat of combustion of benzene at constant volume is $\pu{-3263.9 kJ mol-1}$ at $\pu{25 ^\circ C}$; heat of ...
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### Is it the solution energy or the reduction potentials (or both) that drives a galvanic cell?

I have received conflicting explanations for why the redox reaction in a galvanic cell occurs. Explanation 1: Some say that it occurs because the anodic metal dissolves more easily than the cathodic ... 