# Questions tagged [enthalpy]

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

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### Why is it that the enthalpy of hydration equals the difference of solvation enthalpies of anhydrous and hydrous salts

Taking an example from my textbook At finite dilution of CuSO4, heat is liberated $$\ce{CuSO4(s) -> CuSO4 (aq)}.$$ ΔH of solvation = -15.8 kcal (anhydrous CuSO4 solvation reaction) and when it is ...
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### Combustion Temperature Calculation Using C_p and Heat of Formation

I am simulating the combustion temperature for various compositions of syngas and finding the product temperature. Part one is varying the ratio of CO and H2 from 3:1 to 1:3 in the syngas, burning it ...
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### What is change in enthalpy in energy profile? [closed]

Consider an energy profile diagram. My doubt is that why does change in potential energy (PE) equal change in enthalpy here? At constant pressure change in enthalpy equals the net heat exchanged ...
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### enthalpy of formation of hydronium

Can someone explain how the enthalpy of formation of aqueous hydronium was determined. It appears to be exactly the same as the enthalpy of formation of liquid water. I know this must have something ...
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### Why does it seem that the heat of combustion is higher with substances of greater molecular weights?

Why does it seem that the heat of combustion is higher with substances of greater molecular weights? How do the intermolecular forces or bonds of the reactants affect the heat of combustion? I have ...
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### Sign of Proton Affinity

I was searching for reactions with hydrocarbon anions and hydrogen cation/proton and noticed that the enthalpy change of a reaction is always positive or likewise proton affinity associated with the ...
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### How to find the temperature for when Kc = 1

The formulas I can use are $\Delta$G = H - T$\Delta$S, and $\Delta$G = $\Delta$G(s.t.d) + RTlnK I understand that when Kc is 1, the reaction is barely spontaneous and thus I can use the first formula ...
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### What quantity is one mole in the reaction in enthalpy change? [duplicate]

For example, I have a reaction: $H_2(g)+\frac{1}{2}O_2(g)→H_2O(l),𝛥H=-285.8 kJ mol^{-1}$ What does this "per mole" in the unit represent? What quantity is one mole?
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### What is the effect of temperature on the enthalpy of reaction?

In the study of reaction mechanisms, enthalpy of formation for intermediate compounds at various temperatures is studied. I understand the reason to do that. How much (and what) effect can temperature ...
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### Why we can use ΔH to determine reaction rate in free radical bromination reaction steps?

I am trying to understand why we can use ΔH to determine reaction rate in this a free radical halogenation reaction. Given: (CH3)2CH2 + Br• → (CH3)2CH• + HBr = 397 - 368 = +29 kJ/mol = ΔH (CH3)2CH• + ...
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### I am unable to figure out the reason for first bond enthalpy being higher than second one in water

In $\ce{H2O}$, I am able to understand that the enthalpy needed to break two $\ce{OH}$ bonds are not the same. But I don't understand why is the bond energy for breaking the first $\ce{O-H}$ bond more ...
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### Enthalpy, heat of solution test: Calcium chloride vs magnesium chloride in water

I did a school experiment to measure the heat of solution (enthalpy) of various salts dissolved in water. My results are completely different to the teacher's answer. Specifically my test showed ...
Given the following thermodynamic data at $\pu{298 K}:$  \begin{array}{lrrr} \hline \text{Compound} & \Delta_\mathrm{f}H^\circ/\pu{kJ mol^-1} & S^\circ/\pu{J K^-1 mol^-1} & C_p^\circ/\pu{...