# Questions tagged [enthalpy]

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

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### Standard Enthalpy of Formation of Refrence state(A consequence or assumption) and H+(aq)

Ok, this has been bugging me for a while now. Our teacher taught us that the standard enthalpy of formation of the reference states of elements is "assumed" to be zero. However, I've read in ...
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### Enthalpy change with uncertainties [closed]

Mg + CuSO4 -> MgSO4 + Cu 1.0g Mg and 50ml(=50g) 0.500mol/dm^3 CuSO4 CuSO4 is limiting reactant use q=mcT/mol of limiting reactant and enthalpy change= - q/mol to find the enthalpy change of this ...
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### Two different approaches for calculating enthalpy change for methane + HCl

I know that $\Delta{H}=H_{products}-H_{reactants}$ and also we can use $\Delta{H}=\Sigma{H}_{bonds broken}-\Sigma{H}_{bonds formed}$. Take the example of methane + HCl. If you calculate the total ...
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### The correct way of formulating change in enthalpy

I came across this question: One mole of a non-ideal gas undergoes a change of state $(2.0 atm, 3.0L, 95K)$ to $(4.0 atm, 5.0L, 245K)$ with a change in internal energy = $30L atm$. Find the change in ...
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### If $\Delta$Hsoln < 0, will the conditions for solubility always be met?

If $\Delta$Hsoln < 0, will the conditions for solubility always be met? This was on an exam, and the answer was yes. It could be true, but it seems wrong to me because G=H-TS. So it just seems as ...
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### Why are internal energy and work mentioned in a question about exothermic or endothermic systems? [closed]

This is a question from my chemistry homework. Note the explanation below. A 100.0-g bar of gold is heated from 25°C to 50°C during which it absorbs 322 J of heat. The volume of the gold bar remains ...
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### What is the difference between zero-point and total energy of a molecule in the output of an ORCA FREQ calculation?

I am trying to find the enthalpies of formation for a couple organometallics in ORCA and as a first time user I am a bit bogged down in the terminology. The Gaussian manual has a section on these ...
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### How is temperature inside a bomb calorimeter constant?

I've looked around and have been unable to find an answer. When determining molar reaction enthalpy, you first perform the reaction in the steel bomb then measure the temperature change of the water ...
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### Is ionisation enthalpy physical property or chemical property?

Ionisation enthalpy means energy change when an electron is removed. According to Wikipedia A chemical property is any of a material's properties that becomes evident during, or after, a chemical ...
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### Why does bond energy not vary with position?

Consider the formation of a hydrogen bond: $$\ce{H + H -> H2}$$ The $\Delta H$ is $\pu{-436 kJ mol-1}$, so we can equally write the equation as: $$\ce{H + H -> H2 + \pu{436 kJ}}$$ But depending ...
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### Understanding the Role of Gibbs Free energy and Enthalpy as the energy required to drive a reaction

I was looking at the enthalpy change for water-splitting reaction: $$\Delta H^o_R = [\Delta H^0_{H_2(g)} +\frac{1}{2}\Delta H^0_{O_2(g)}]-\Delta H^0_{H_2O(l)} = \pu{285.83 kJ/mol}$$ According to ...
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I came across a question asking to indicate the enthalpy of solution for a solution of 1-pentanol in 1-butanol. The options were the following: $\Delta H < 0$ $\Delta H \approx 0$ $\Delta H >... 0 votes 0 answers 68 views ### What exactly is meant by standard state in thermodynamics? [duplicate] I was told that the standard enthalpy of a reaction is the enthalpy change when the reaction occurs with all reactants and products being in there standard states and under standard conditions(1 bar ... -3 votes 1 answer 76 views ### calculation of enthalpy change So for for the calculation of$\Delta{H}$,we have two formulaes in our book:$\Delta{H}=E_{2}-E_{1}$where$E_{2},E_{1}$are the internal energies of the product and reactants respectively. Now this ... 2 votes 0 answers 90 views ### Discrepancy between calculated and experimental enthalpy change of formation? Hydrogen Iodide Afterthought: See edits below! $$\ce{1/2 H2(g) + 1/2 I2(g) -> HI(g)} \qquad \Delta_\mathrm f H^\circ=26.5\ \mathrm{kJ\ mol^{-1}}$$ source: https://atct.anl.gov/Thermochemical%20Data/version%201.... • 494 1 vote 2 answers 187 views ### Physical meaning of term T∆S Plot "I assume the role of an attentive observer, carefully watching a chemical reaction unfold within a sealed container. This enclosed environment, completely closed ( no matter but energy can ... 0 votes 1 answer 455 views ### Why does Cr have higher melting point in the 4 period among the transition metal? [duplicate] There is a lot of answer stating that the low enthalpy of atomisation in Cr is due to the reason of partially filled d orbital, thus having extra stability. This makes the orbital more attracted ... 1 vote 1 answer 255 views ### How to Calculate Entropy Changes at Non-Standard Conditions I am trying to calculate the values of$\Delta H$and$T\Delta S$for the reaction taking place at$\pu{800 ^\circ C}$$$\ce{CO2 + H2O + 2CH4 -> 3CO + 5H2}$$ I calculated$\Delta H$to be$\pu{\...
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What I want to know is about the adsorption enthalpy change by the change of surface coverage and the adsorption rate. In general situations, adsorption would be exothermic. So in the Gibbs free ...
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### What do the units of enthalpy kJ/mol represent?

Enthalpy is making me slightly confused. Here $\Delta H$ refers to the change in enthalpy. Does this refer to the enthalpy change of reaction? Are they the same? It seems that change in enthalpy, ...
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### Enthalpy change of neutralisation?

Consider this problem. The enthalpy of neutralisation is defined as the enthalpy change when one mole of water is formed through the react of an acid and base at standard conditions. As the ...
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### How is the reason for “why neutralizing weack acids with strong bases gives less heat” that the heat is used in ionizing the acid?

In my lab manual this is written but I can’t see how this is true The heat of neutralization of weak acids by strong bases is less than 13.7 Cal/mole because the weak acid becomes completely ionized ...
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### Why does an exothermic/endothermic reaction have a negative/positive enthalpy

So regarding change in enthalpy and exothermic/endothermic reactions, I think I have some conceptual understanding but I'm missing some things. My current understanding is that: Given a reaction, if ...
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### Is change in enthalpy heat supplied at constant internal or external pressure? [closed]

From what I understood, we introduced enthalpy to work with reactions that were carried out at constant external pressure. But then I came across this formula (for ideal gas): ∆H=∆U + p∆V where p∆V=∆...
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### Why is the first electron affinity exothermic and successive ones endothermic?

I am having trouble wrapping my head around electron affinities. And the textbook explanations aren't very helpful. So, the textbook says that the 1st electron affinity is generally exothermic. The ...
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