Questions relating to heat and its relation to other forms of energy in chemistry.

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1answer
10 views

Reversible or irreversible process [on hold]

If there is a process in which a gas is being expanded against a constant pressure (ie the pressure of the atmosphere is constant before the process, during the process and after the process), then is ...
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0answers
18 views

why is the term enthalpy created? [on hold]

Giving heat to a system changes its intrernal energy.Then why is the term enthalpy created?Change in internal energy must be the total heat gained or lost then why in heat capacity at constant ...
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0answers
21 views

Estimate specific heat capacity of liquid [on hold]

I am attempting to help a friend with thermodynamics homework, but I am unfamiliar with questions like this. I am given this question: A calorimeter of mass 90 g and specific heat capacity $420\ ...
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0answers
45 views

Gibbs Free Energy and entropy of the universe

I'm having a little bit of trouble after putting alot of thought into the relationship between entropy of the universe and Gibbs Free Energy. Both are used to predict spontaneity, but from my ...
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2answers
44 views

A problem from thermodynamics

I am trying to do the following problem: Freezing of water at $273~\mathrm K$ and $1~\mathrm{atm}$ Which of the following is true for the above thermodynamics process? p) $q=0$ q) ...
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1answer
71 views

Doubt regarding the second law of thermodynamics [on hold]

$$\frac{q_{rev}}{T} = \Delta S$$ Here, what does $\Delta S$ signify? Does it mean the change in entropy of the system or the surroundings? How are the entropies of the system, the surroundings, and ...
3
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0answers
35 views

Calculating the electrode potential from thermochemical data

How can I calculate the electrode potential from thermochemical data? My attempt: I know that the electrode potential is dependent on the enthalpies of: atomisation, first ionisation, second ...
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0answers
16 views

Calculating entropy change when heating a solid [on hold]

I got a question on a test, as such : Assume we have 1 mole of a solid, all units in J. Also assume ideal crystal solid has 0 entropy at 0K. Suppose the absolute entropy of a solid at 100K is 20J. ...
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2answers
26 views

Assumptions made in calculating melting point from thermodynamic data

I'm fine with doing these questions, such as: For ammonia, enthalpy of fusion is 5.65 kJ/mol, and entropy of fusion is 28.9 J/K.mol Hence find an approximate melting point: Well $\Delta G = \Delta H ...
3
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0answers
15 views

Steric hindrance of an unbonded electron pair

This question is half inspired by this question, and half inspired by the structure of molecules like hydrazine and hydrogen peroxide. When I was looking at the aforementioned molecules, I started ...
1
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1answer
25 views

Specific Heat affected by Pressure

I know the specific heat depends (slightly) on the conditions present. For example, methane's specific heat is 2.5 at 400 K, but 4.5 at higher temperatures. How might specific heat depend on ...
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0answers
11 views

Energy in Reaction Profile [closed]

What is the difference between the Reaction Profiles when they have 1) Potential Energy 2) Gibbs Free Energy 3) Enthalpy
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0answers
25 views

Relationship between Gibbs free energy, enthalpy, entropy and rate of reactions

I'm having a little trouble constructing the bigger picture of chemical reactions. From the collision theory we know that molecules react if: 1) they collide 2) they collide bearing a sufficient ...
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0answers
24 views

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 ...
3
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2answers
149 views

Why are there different values for enthalpy of combustion, depending on the calculation method?

For example: Combustion of Ethanol $\ce{C2H5OH(l) + 3O2(g) -> 2CO2(g) + 3H2O (l)}$ If i calculate this using enthalpy of formation: $\begin{array}{c|c} \textrm{Substance} & \Delta \ce{Hº ...
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1answer
24 views

Why do liquids freeze into a polycrystal solid when they freeze fast?

I don't see any possible explanation. If there's a crystallite at one orientation, why would a crystallite at another orientation start growing instead of more molecules just building onto the surface ...
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0answers
26 views

What is the meaning of the double tilde in the enthalpy diagram?

My highschool book presents this diagram. I have searched the web and did not found the meaning of this ~~ tildes on y-axis.
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0answers
31 views

“Reacts most vigorously”

What is meaning of "Reacts most Vigorously" Is it related to Thermodynamic aspect or Kinetic? Like for example if we are given that A reacts with C more vigorously than B reacts with C. Then which ...
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1answer
23 views

Determining the temperature at which 90% of the reactants in a equilibrium have reacted

I have the following problem I am stuck on, specifically the last bit (iii). The first parts are fairly trivial and I have arrived at the following equation to determine the temperature: ...
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0answers
26 views

Gibbs Free energy Process v/s Reaction

How is Gibbs free energy for a reaction different from that in a process? Is it because a reaction generally occurs at a constant temperature and pressure, and so dG = dH - TdS, while for a process ...
3
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2answers
61 views

How can a nonspontaneous reaction occur?

$$\frac{-\Delta G}{T}=\Delta S_{universe}$$ (This equation applies under isobaric and isothermal conditions.) I understand that if $\Delta G$ is positive, the reaction is nonspontaneous, and adding ...
0
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1answer
84 views

Calculating temperature after adding heat to ice

If $53.2~\mathrm{kJ}$ of heat are added to $15.5~\mathrm{g}$ of ice at $-5^\circ\mathrm{C}$, what will be the resultant state of matter in which water is present and also calculate its final ...
0
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1answer
40 views

Enthalpy change vs. change in internal energy in a system

I've been trying to get my head around the differences between enthalpy change and internal energy change for a system. Here's my understanding of it so far. I'd appreciate any feedback on my ...
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0answers
21 views

Minimizing Gibbs Free Energy for Multiphase Equalibria

I'm a geologist and don't have a strong background in chemistry or thermodynamics. Any help on solving this problem is much appreciated. I'm trying to minimize Gibbs free energy to get initial ...
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0answers
10 views

Halving the electrolyte concentrations of a voltaic cell

Say you have a standard voltaic cell with $Q=1$. The concentrations of both the electrolytes are at 1.0 M. If you halve the concentrations in both to 0.5 M, $Q$ still equals 1 and ...
0
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1answer
22 views

The equilibrium constant of a reaction only involving pure solid or liquid

How to calculate the equilibrium constant of a reaction only involving pure solid or liquid. For example reaction $$\ce{S(s) + Hg(l) -> HgS(s)}$$ or $$\ce{S(s) + Mg(s) -> MgS(s)}$$
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2answers
23 views

Enthalpy change defined at constant pressure only?

Is change in enthalpy defined only at constant pressure? I know Q-W=del(U) And Q at constant pressure equals del(H) (enthalpy change). Can Q (heat given to the system) be used interchangeably ...
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0answers
14 views

Difference between bulk free energy and cohesive enrgy

I am writing a lammp's code to calculate size dependent surface energy of FCC copper nano particles. First of all I need to calculate total bulk energy of each atom in the crystal. my question is that ...
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4answers
50 views

Why do liquids vaporise spontaneously at temperatures below boiling point despite ∆G being positive?

We say that for the equilibrium $$\ce{A(l)<=>A(g)}$$ the ∆G is zero at its boiling point (the thermodynamic definition of boiling point), and becomes positive at temperatures below the boiling ...
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2answers
54 views

Does exothermic solvation mean solute is more soluble at low temp?

(I'm surprised this question or a very similar one hasn't been asked, so I wouldn't be surprised if I just failed to find a question with my search that does answer this question.) I dissolved some ...
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1answer
49 views

How does salt help with −30 °C cold ice?

I know that ice gets colder when salt is added. But how big is the effect if it is already −30 °C? Can it cool it down more or does it just work with −1 °C cold ice? Another question: If I have a ...
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3answers
66 views

Intuition on Gibbs Free Energy

In many places, I read that Gibbs Free Energy is called "free energy" because some of the enthalpy that comes from the chemical reaction becomes "waste heat" due to a change in the entropy of the ...
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1answer
46 views

Is water committed to vapor state at boiling point or after? [duplicate]

Quite early into my studies, I learnt about phase changes with this graph. I’m just going to focus on vaporization/condensation. I learnt that the plateau was caused because all the heat was going ...
4
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1answer
103 views

How to treat pressure in computational chemistry?

I have a reaction where a gas at high pressure and a solution with all kinds of species is involved. How do I take pressure correctly into account to get reasonable values for $G$? Do I calculate ...
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2answers
63 views

Deriving an expression for the constant pressure heat capacity

Given the relation $G = H − T S$, show that: $$\left(\frac{\partial S}{\partial T}\right)_p=\frac{C_p}T$$ Now I realise that $T\mathrm dS=\mathrm dQ$ and that would I suppose get the result. ...
2
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2answers
32 views

Ionization Energy and Electron Affinity

This is from my textbook. But in other reference books I am using and Wikipedia, there is not any mention of absolute zero while defining Ionization Energy and Electron Affinity. What does it mean? ...
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0answers
37 views

Adding reduction potentials?

Will it be wrong to add reduction potentials of two intermediate reactions to get reduction potential of net reaction(just like as we do in adding enthalpies and applying Hess's law)? What is the ...
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0answers
15 views

Thermodynamics of mixture of gases and gas to liquid transformation of particular gas in mixture of gases

I am working on converting the nitrogen and sulphur dioxide from gas to liquid in the mixture of $\ce{CO2}$, nitrogen and sulphur dioxide. For continuous conversion from gas to liquid phase, I want to ...
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0answers
16 views

Are all chemical reaction taking place isobaric?

since all chemical reaction take place in open and there is no appreciable change in pressure because atmospheric pressure is constant,so can we say all chemical reactions are isobaric in nature?
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20 views

How do you find the heat capacity of a calorimeter?

My instructor gave me the formula: $$C_\mathrm{cal} = \frac{C_\mathrm{bomb}}{\text{steel}+C_\mathrm{water}}$$ I know that the heat capacity for water is $4.184~\mathrm{J\,g^{-1}\,^\circ C^{-1}}$ and I ...
4
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2answers
54 views

Safe endothermic reaction that gets below freezing?

I have a project/idea I am working on but I am only 14 years old and I need some help. I'm looking for an endothermic reaction that gets below freezing, but the chemicals before the reaction and ...
3
votes
1answer
32 views

Le Chatelier's with pure solids and liquids

In the following general reaction, $$\ce{A(s) <=> B(g) + C(g)}$$ since adding a pure solid is not supposed to shift the equilibrium in any way, does that mean that I can essentially remove all ...
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1answer
69 views

Internal energy calculation

The temperature of 1 mole of a liquid is raised by heating it with 750 joules of energy. It expands and does 200 joules of work, calculate the change in internal energy of the liquid. I want to ...
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0answers
28 views

Calculating temperature change of mixing two acids with different concentration

I need to predict what will be final temperature of solution after mixing two H2SO4 solutions with different concentrations. What effects I have to account for? Do I simply calculate this as if I ...
0
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2answers
51 views

derivation of enthalpy internal energy relationship [closed]

A question asks us to derive a relationship between the enthalpy change and the change in internal energy for a reaction. Now, I know the relationship is: $\Delta H = \Delta U + V \Delta p + p \Delta ...
3
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0answers
38 views

Why does the temperature of the gas in a container moving with constant velocity does not change? [closed]

Systematic changes do not affect thermodynamic equilibrium. What does this mean? And what kind of systematic changes are allowed? The container with gas is stationary till some time then its ...
1
vote
1answer
45 views

On stretching a rubberband does the entropy increase or decrease?

It seems that on stretching a rubberband, entropy or the degree of disorder is likely to increase. Is this the correct answer? My text says that on stretching, the arrangement of particles become more ...
1
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1answer
52 views

heat capacity at constant volume and internal energy

I read that heat supplied at constant volume to a system containing ideal gas changes the internal energy of system i.e $q=n C_v \Delta T= \Delta U$ But what happens if I heat a system and change its ...
6
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1answer
207 views

Why is adsorption exothermic

Why is adsorption exothermic? The explanation given in my textbook is: It basically says adsorption is exothermic because $\Delta G$ has to be negative. Isn't there any other reason?