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Questions tagged [thermodynamics]

Applicable to questions about heat, energy, work, and their interconversion in chemistry. See the tag wiki for a detailed list of topics. Questions tagged may also be tagged with [enthalpy], [energy], [free-energy] where appropriate.

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How does pH change during the electrolysis of water? [closed]

How does the pH change during electrolysis of a water and magnesium sulphate solution? Also, will this pH change happen every time? Does the pH change differently when there is just water in the ...
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1answer
72 views

Thermodynamics energy balance question help

I made the following attempt to solve this question.However I don't know how to find final pressure.I don't know how to find final temperature for both sides.Can you give me a hint?
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2answers
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In what approximations, if any, can we assume a constant temperature in a Bomb calorimeter?

In most, if not all, general chemistry books, you will find that in from constant volume calorimeters, $\Delta H = \Delta U + RT \Delta n_\mathrm{g}$, which is, of course derived from $H = U + PV$. ...
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1answer
307 views

What is the reason behind the phenomenon of Joule-Thomson effect?

For an ideal gas there is no heating or cooling during an adiabatic expansion or contraction, but for real gases, an adiabatic expansion or contraction is generally accompanied by a heating or cooling ...
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2answers
181 views

Is dH work dependent?

In the equation $\ce{d}H=\ce{d}U+\ce{d}(PV)$ Under constant pressure is $\ce{d}(PV)$ equal to the work done ($W$) on the system? (where $W= P_{\text{ext}}\mathrm{d}V$ (for irreversible process) and ...
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0answers
128 views

Deriving a relation between entropy, volume and particles through the chemical potential

I'm a teaching assistant on a first year course on Introduction to Thermodynamics based on the book "Molecular Driving Forces" by Dill & Bromberg. There's a question which asks the students to ...
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1answer
1k views

Standard state of a substance - definition

In chemistry, the standard state of a material (pure substance, mixture or solution) is a reference point used to calculate its properties under different conditions. IUPAC recommends using a standard ...
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1answer
1k views

What is the difference between enthalpy of reaction and standard enthalpy?

What is the difference between enthalpy of reaction ($\Delta H$) and standard enthalpy ($\Delta H^\circ$)? I was told that the standard enthalpy of reaction is the change in heat when one mole of ...
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2answers
154 views

Why does increasing temperature for an endothermic reaction always increase equilibrium constant?

According to Le Chatelier's Principle, increasing temperature for an endothermic reaction shifts the reaction towards the products. However, unless there are things that I am missing, I believe there ...
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0answers
47 views

Can a droplet of formalin evaporate in midair while falling?

I am designing an evaporator for use in an enclosed environment. Due to the hazardous nature of formaldehyde, I want my evaporator to be wick-free. The environment in which the evaporator will be used ...
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1answer
52 views

Enthalpy of formaton [closed]

today I was doing a set of HW problems regarding enthalpy and stumble upon one problem that I found confusing.It was the standard enthalpy of formation for CaCO3 is -1207.6 kJ mol when 30.7 g of ...
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0answers
52 views

Is chemical equilibrium possible at any temperature and pressure?

Consider the chemical reaction ${\rm Na+Cl\to NaCl}$ by mixing ${\rm Na}$ with ${\rm Cl}$ (or by mixing ${\rm NaOH}$ with some acid). This process is exothermic while the reverse ${\rm NaCl\to Na+Cl}$ ...
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2answers
934 views

How would one calculate the entropy change for an adiabatic irreversible process?

If two states $A$ and $ B$ are connected by a reversible path, they can never be connected by an irreversible path during an adiabatic process because: $\underbrace{\Delta U}_{\text{state function}} ...
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1answer
429 views

Can pressure remain constant in isothermal expansion?

An ideal gas undergoes isothermal expansion at constant pressure. During the process: enthalpy increases but entropy decreases. enthalpy remains constant but entropy increases. enthalpy ...
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0answers
31 views

Would a reaction always occur if the change in its Gibbs free energy is negative? [duplicate]

Would a reaction always occur if the change in its Gibbs free energy is negative? Other than coupled reactions, is this always true? An example is conversion of ozone to dioxygen. It is exothermic ...
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1answer
2k views

What do “degrees of freedom” refer to?

Can you explain simply what are the degrees of freedom in chemistry? I don't fathom it very intuitively from Wikipedia. I have almost no background in physics. I understand that it refers to all the ...
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0answers
367 views

Is a low specific heat capacity for the material of the calorimeter good or bad?

I wish to ask if a low specific heat capacity of the material of the calorimeter means that the calorimeter would be more exact as it takes less heat for the material to reach equilibrium. I thought ...
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0answers
60 views

Finding Overall Entropy Change

Find the entropy of the overall reaction \begin{align} \ce{S8 (s) + 8 O2 (s) &-> 8SO2 (g)}& S &= \pu{89 J/K }\\ \ce{2SO2 (s) + O2 (s) &-> 2SO3 (g)}& \Delta S &=...
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1answer
172 views

Why might copper have a lower heat capacity than lithium according to the Shomate Equation?

I've learned that according to Condensed phase thermochemistry data, according to NIST, the functions of heat capacity, enthalpy, and entropy can be predicted by the Shomate Equation: $$\begin{align} ...
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2answers
113 views

Work equation in thermodynamics

As known, work done on the system is: $$\mathrm{d}W = -P_{\text{ex}}\mathrm{d}V $$ However, I have some ambiguity about this equation: Why is there $P_{\text{ex}}$? Pressure of a gas contained in a ...
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2answers
117 views

Is the equilibrium constant in the expression based on pressure or concentration?

$$\Delta G^\circ=-RT\ln K$$ I have always assumed it to be $K_p$ because $\Delta G^\circ$ represents standard free energy change and the standard state for a gas is 1 bar. So I thought we must ...
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1answer
290 views

Phase diagram of water using Gibbs free energy instead of pressure [closed]

From my lecture course it was indicated that this is what a phase diagram looks like. Is this diagram applicable to water? All the ones I can find online seem to use pressure on the y axis as oppose ...
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1answer
2k views

What is non PV work? How is it related to Gibbs energy?

Recently, I was trying to understand more about Gibbs free energy and got stuck at this point. Some books write that if $\Delta G=0$, then the reaction is reversible while some other sources say that ...
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1answer
92 views

Significance of Temperature in Gibbs Free Energy

Why is it important to know the temperature of both reactants and products of a reaction in order to determine change in the Gibbs free energy of the reaction? Is it because temperature has an effect ...
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1answer
537 views

How does change in entropy influence the tendency of a reaction to occur? [duplicate]

I know that entropy is the measure of the randomness of particles within a system, but how would it affect the tendency of the reaction? Would it just increase or decrease the chance of the reaction ...
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2answers
173 views

What are the units that measure free energy?

Is it $\pu{kJ/mol}$? I have done problems and I always end up with these units, but is this correct?
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2answers
54 views

Can we produce tritium from helium 3? If yes how?

I want to know the best and economic way of the manufacture of tritium from helium-3
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1answer
217 views

How can a decomposition reaction be exothermic?

Decomposition reactions involve breaking of bonds which requires energy. Therefore, they are generally endothermic. But how can decomposition reactions release energy? Examples are the respiration ...
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0answers
36 views

Why is the activation energy for 1,2-addition less than that for 1,4-addition to conjugated dienes?

1,2-addition proceeds faster than 1,4 addition making excess of 1,2-adduct at low temperatures. Also, since conversion of 1,2-adduct to 1,4-adduct is faster than the reverse, 1,4-adduct is in excess ...
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2answers
655 views

Is it possible to determine the absolute value of entropy of a system?

I came across a question (in some assignments I had received) where it was asked: Can the absolute value of entropy of a system can be measured? and to my surprise, the answer said yes. Till now, ...
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2answers
195 views

Expansion under isobaric adiabatic condition

A 3 mole sample of a triatomic gas at $\pu{300 K}$ is allowed to expand under isobaric adiabatic condition from $\pu{5L}$ to $\pu{40L}$. The value of change in enthalpy is: $\pu{12.46 KJ}$ ...
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2answers
109 views

Can the change in the entropy of the surroundings always be obtained by dividing heat transferred by the temperature at which the transfer occurs?

Consider $\pu{1 mol}$ of an ideal monoatomic gas going through reversible isochoric heating from $\pu{100 K}$ to $\pu{1000 K}$. Calculate $\Delta S_\pu{sys}, \Delta S_\pu{surr}.$ $$\Delta S_\pu{...
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2answers
797 views

What are the degrees of freedom (from Gibbs phase rule) for an azeotropic mixture?

For an azeotropic binary mixture, the number of phases is 2 and number of components are 2. So, according to Gibbs phase rule, the number of degrees of freedom should be 2. But, the right answer is 1. ...
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1answer
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Is Internal Energy = (3/2)nRT for a ideal monoatomic gas?

Internal Energy is a state variable and its value at a particular state cannot be measured; only the change in internal energy can be measured. So how come we write that $$U=\frac32nRT$$ where $U$ = ...
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2answers
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Why 'Enthalpy change' (Delta H) is equal to 'Heat transfer at constant pressure' (Qp)? [closed]

Why 'Enthalpy change' (∆H) is equal to 'Heat transfer at constant pressure' (Qp)? ∆H = ∆U + ∆pV, here only expansion work done by the sustem is added. If non expansion work is done on the system then ...
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1answer
667 views

What does the shaded area represent?

I'm not sure what the answer is, all of my friends and my chemistry teacher said it is A, I think it is obvious that the graph is talking about 2 catalysts so it could be D. But I have no idea what ...
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0answers
29 views

Inernal energy with e=mc^2 [duplicate]

If we knew the mass of system we can calculate internal energy by using Einstein equation e=mc^2 and get value of internal energy What is mistake in my approach??
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1answer
513 views

can a thermodynamically unfavorable reaction be made favorable by a catalyst?

The question i am asking about is pertaining simply to chemical use of a catalyst. It drives a reaction along a different path without taking part chemically. I know this fact. Is it possible so like ...
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1answer
20 views

How do you work out the amount of energy which will be released when a substance undergoes combustion in a pure oxygen environment [closed]

For instance, if we have an abundance of pure Oxygen and one kilogram of Hydrogen and all the Hydrogen reacts with the Oxygen to form H20, how do you work out the amount of energy which will be ...
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1answer
59 views

What's the actual or official definition of activation energy? [duplicate]

In some sources I have seen that activation energy is the minimum energy required to cause a reaction. This implies that activation energy doesn't change with temperature (not considering very high ...
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1answer
1k views

Relation between R and k [closed]

$R$ is the universal gas constant equaling $8.314\ \mathrm{J/(mol\ K)}$. $k$ is the Boltzman constant equaling $1.38\times10^{-23}\ \mathrm{J/K}$. $$R=nk$$ $n$ is no. of moles. $n$ can change. $R$ ...
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1answer
54 views

How does atomization allow droplets to evaporate below their boiling point, cooling the surrounding vapor to an even lower temperature? [closed]

I understand why the vapor is cooled in such a scenario, because of the heat required to change states, but I don't fully understand why the state change even occurs if below the BP. Why does it seem ...
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2answers
470 views

Entropy is a measure of unavailable energy?

I came across a statement in my text book which said that entropy is a measure of unavailable energy. What does this statement signify?
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1answer
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How does the mathematical definition of entropy (ΔS=Qrev/T) give us the degree of disorder? [closed]

I think degree of disorder in thermodynamics means the number of possible locations that a molecule can take How does the mathematical equation signify this?
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1answer
31 views

Thermal vibration of bonds [closed]

So, the characteristic frequency of thermal motion is around 7E12 Hz at room temperature (300K), but from that information how can we conclude that the bonds are hard; they don't vibrate !!
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2answers
333 views

Physical significance of magnitude of ΔG (Change in Gibbs Free Energy) of a reaction [closed]

In thermodynamics, we know that if ΔG of a reaction is -ve the reaction is spontaneous. Suppose we are given with 2 spontaneous reactions (ΔG<0) with corresponding magnitudes of ΔG. Can we extract ...
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2answers
105 views

Is there an example where interpreting reaction coordinate as time leads to an incorrect conclusion?

I have heard that we should not interpret the reaction coordinate in an energy diagram as time, but are there any situations in which we would arrive at an incorrect conclusion if we did so? When I ...
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1answer
110 views

Dropping Borosilicate glass mug

I recently got a glass tea mug. It's has double wall construction with a vacuum insulation (advertised as such). I noticed on the label, it specifically mentioned it's made of borosilicate glass, and ...
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1answer
123 views

What is the mass of (NH4)2CO3 need to add to 250 g water in order to lower the freezing point approximately 5.5 °C? [closed]

What is the mass of $\ce{(NH4)2CO3}$ need to add to $250\ \mathrm g$ water in order to lower the freezing point approximately $5.5\ \mathrm{^\circ C}$? $K_\mathrm f=1.86\ \mathrm{^\circ C\ kg/mol}$ ...
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0answers
29 views

How is the number of successful collisions in a time-step distributed?

In a spatial homogeneous reaction system with two different molecules, how is the number of collisions which will lead to a reaction in a fixed time-step distributed? My guess: Poisson distribution, ...