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.

Filter by
Sorted by
Tagged with
1
vote
0answers
25 views

Are there any exceptions to Le Chatelier’s principle? [duplicate]

Peter Atkins says In introductory chemistry, we meet the empirical rule of thumb known as Le Chatelier’s principle: When a system at equilibrium is subjected to a disturbance, the ...
0
votes
0answers
29 views

Calculate change in entropy when both temperature and volume change

Calculate the change in entropy when $\pu{23.5 g}$ of oxygen gas is heated from $\pu{240 K}$ to $\pu{360 K}$ in such a way that its pressure increases from $\pu{2.00 kPa}$ to $\pu{8.00 kPa}.$ Assume ...
0
votes
0answers
45 views

Finding the temperature at which the system reaches equilibrium

I’m really stuck on this problem. This involves dissolving Borax: $$\ce{Na2B4O7•10H2O(s)<=>2Na^+(aq) + B4O7^2-(aq) + 10H2O}$$ $$\begin{align}\Delta H&=\pu{109 kJ/mol} \\ \Delta S&= \pu{...
-1
votes
2answers
59 views

What are the system and surroundings when dissolving sodium nitrate in water?

When sodium nitrate ($\ce{NaNO3}$) dissolves in water at room temperature, the solution cools down. $\Delta H$ is positive because heat flows into the system during the process. I thought though, ...
1
vote
0answers
37 views

Issue with evaporation rate of water

The evaporation rate of water (kg/s) is given by: $$g = \frac{P}{P_o} AΘ$$ Where $P$ is given in Pascals and $A$ is the surface area (in $m^2$) and $Θ$ is the empirical evaporation ...
0
votes
1answer
25 views

Regarding enthalpy of a reaction

Enthalpy of a reaction $$\ce{2H2 (g) + O2 (g)-> 2H2O(g)} \Delta H_1$$ $$\ce{2H2 (g) + O2 (g)-> 2H2O(l)} \Delta H_2$$ Now I was asked to compare the enthalpy. If I subtract reaction 2 from 1, ...
1
vote
0answers
14 views

Reaction enthalpy using bond energy in resonating molecules

To find out and enthalpy of a reaction using bond energy we use the formula $$\Delta H = \sum\Delta_\mathrm{bond}H_\mathrm{reactants} - \sum\Delta_\mathrm{bond}H_\mathrm{products}$$ since we use all ...
1
vote
1answer
44 views

Temperature and pressure for three phase equilibrium of aqueous sodium chloride solutions

I am currently investigating the effect of adding Salt(NaCl) to water on its triple point. Let us assume the mass ratio of water to NaCl is $1:1$. I asked a similar question previously. But, I still ...
2
votes
1answer
81 views

Energy absorbed by a system in isothermic process in which the phase changes from liquid to gas

A system contains $x$ mole of material, with surface area $S$ is pressed by a mass $M_1$ (no fraction and no any other outer forces involves). Let $\Delta H_\mathrm{l\rightarrow g}$ be the transition ...
0
votes
0answers
32 views

intuitive explanation of Wegscheider condition and its violation

The Wegscheider condition restricts the values that rate constants in a set of chemical reactions can take on. can someone please explain intuitively why the condition has to be true, and give a ...
13
votes
1answer
130 views

Why does ordinary water have a triple point?

Triple points and triple lines for pure substances and mixtures My understanding is that pure substances can have triple points. But mixtures of substances have triple lines, i.e. there isn't a ...
2
votes
2answers
87 views

Does adding solutes to water alter its triple point? [closed]

Does adding solutes to water alter its triple point? If yes, how do we find the new temperature and pressure of this point?
4
votes
1answer
119 views

How to get the efficiency of a heat engine which undergoes an elliptical cycle?

An ideal diatomic gas undergoes an elliptic cyclic process characterized by the following points in a $PV$ diagram: $$(3/2P_1, V1)$$ $$(2P_1, (V1+V2)/2)$$ $$(3/2P_1, V2)$$ $$(P_1, (V1+V2)/2)...
0
votes
2answers
55 views

Statistical thermodynamics [closed]

Entropy of indistinguishable particles $S$ is $$S = k\ln W,$$ but in some places notation is different: $$S = k\ln Q + \frac{U}{T}$$ Can you explain, please?
3
votes
2answers
94 views

What mixing ratio of ethanol and acetone has the lowest freezing point?

I am in the lab trying to make a sample for 1H NMR. It has to remain liquid at the lowest possible temperature. I was recommended to use a mixture of ethanol and acetone because when they're mixed in ...
3
votes
1answer
64 views

Why does the solubility of LiCl increase with temperature if the dissolution is exothermic?

In an answer to another question, the following data on the solubility of $\ce{LiCl}$ at different temperatures is presented. This suggests that dissolving LiCl is endothermic (according to the ...
2
votes
3answers
126 views

How to explain disagreement between Le Châtelier's principle and the simplified Gibbs free energy equation?

For example, for the dissolution of a salt in water that is exothermic, heating the solution would drive the reaction towards the solid form of the salt according to Le Châtelier's principle. However,...
2
votes
3answers
83 views

Where does the energy come from to lower the temperature of a brine solution?

Suppose I have a densely packed bucket of ice chips / cubes made from pure $\ce{H2O}$. It has been at room temperature for days, so the interior temp of the ice is likely close to 0 °C / 32 °F. (I ...
0
votes
1answer
25 views

How would a temperature profile in wall change if the rate of heat transfer increases

Given the system below, how would the temperature profile in the wall change if the heat transfer in Fluid II was very fast? If the heat transfer in Fluid II is very fast, then the T-profile ...
0
votes
0answers
62 views

How to calculate the variation of the standard reaction enthalpy for the CO, CO2, H2O, H2 equilibrium?

For the reaction $$\ce{CO2 (g) + H2 (g) <=> CO (g) + H2O (g)}$$ the equilibrium constant $K_p$ has a value of $0.534$ at $\pu{960 K}$ and $1.571$ at $\pu{1260 K}$. Calculate the variation of ...
1
vote
1answer
84 views

Are there more endothermic or exothermic reactions? [closed]

I'm wondering whether there are more endothermic or exothermic reactions. Of course the amount of mass will stay the same, but I thought that not every exothermic reaction has an endothermic counter-...
2
votes
0answers
50 views

Is it appropriate to approximate solute particles in a dilute solution as an ideal gas?

I was studying osmosis and I came across the formula for osmotic pressure. I decided to see the derivation for osmotic pressure in a dilute solution. The derivation involved an equation involving the ...
1
vote
2answers
74 views

Do maxima in Gibbs energy also correspond to equilibrium positions?

ΔrG=(∂G/∂ξ ) at constant p and constant T, where ξ is the extent of reaction. By Second Law implication, ΔrG= 0= (∂G/∂ξ ) at equilibrium. If we consider a graph of G against ξ, this would mean we ...
-6
votes
2answers
145 views

Why is Avagadro's number independent of substance? [closed]

In the book of Irey, Thermodynamics, in vol1, IA, page 4, it is given that Molecular (atomic) weight $M$: The ratio of the mass of a molecule (atom) of a substance to one twelfth of the mass of an ...
6
votes
1answer
180 views

How does increase in volume change the speed of reaction in production of NO2?

$$\ce{2 NO + O2 <=> 2 NO2}$$ I understand that increasing the volume $×2$ means lower pressure so production of $\ce{NO2}$ is slowed down, but when asked how to express this mathematicaly I can'...
3
votes
1answer
78 views

What actually happens when 'energy is released'? [duplicate]

Thermodynamics classes and equations always discuss a chemical reaction in the form of energy being released or absorbed. This is always hand-waved as just 'energy' from the surroundings. What's ...
3
votes
1answer
70 views

Relation between equilibrium constant and entropy change

Like the Van't Hoff equation, which relates change in enthalpy to equilibrium constant, is there a similar equation for the relation between change in entropy and equilibrium constant? Consider the ...
0
votes
2answers
73 views

Reaction quotient and Gibbs free energy at the start of a reaction

According to the equation 33 above, shouldn't be all the reactions be spontaneous initially? Because the reaction quotient Q, is zero at the start of the reaction and logarithm of Q makes it a very ...
3
votes
1answer
95 views

Why is nitroglycerin so unstable?

I know that nitroglycerin is an incredibly powerful explosive due to its three nitro groups, but why is it so unstable? What in its chemical structure makes it so sensitive to shock and temperature? ...
2
votes
1answer
63 views

K in Gibbs free energy

When we write for an equilibrium that $$\Delta G^\circ = -RT \ln(K)$$ Which type of $K$ , ie is it $K_\text{concentration}, K_\text{pressure}$ or $K_{\chi}$ because all these have different numeric ...
1
vote
1answer
67 views

Thermodynamics: ΔU = Q + W or U = Q?

Heat is the total kinetic energy of all atoms of the system. When work is done on the system it means that a part of system kinetic energy is used to do the work, and this work makes the surrounding ...
2
votes
0answers
44 views

Hydrogen + Fluorine Adiabatic Flame Temperature

The theoretical adiabatic flame temperature of Hydrogen and Fluorine in their stoichiometric mixture is often quoted at around $\pu{4300K}$, such as in this presentation on page 2, or this paper which ...
1
vote
1answer
70 views

Why does the rate of the reaction decrease with an increase in temperature?

Why does the following reaction $$\ce{2NO + O_2 -> 2NO_2}$$ have negative reaction coefficient, i.e., why does the rate of the reaction decrease with an increase in temperature ? I have been ...
4
votes
3answers
142 views

Calculating ΔG at the extremes of reaction extent

This question follows on from a great post on comparing $\Delta_\mathrm{r} G^{\circ}$ to $\Delta_\mathrm{r} G$ answered here The G vs ξ graph that is used in the answer is an excellent tool to ...
0
votes
1answer
30 views

Can somebody explain the low temperature Schottky anomaly for two level systems?

Statistical thermodynamics question. Can somebody explain the low temperature Schottky anomaly for two level systems? Why is this anomaly not seen in all materials?
4
votes
3answers
343 views

If change in free energy (G) is positive, how do those reactions still occur?

I was doing a couple of problems for homework: Calculate $K_\mathrm{sp}$ of $\ce{AgI}$ at $55.0\ \mathrm{^\circ C}$ Calculate $K_\mathrm{b}$ of $\ce{NH3}$ at $36.0\ \mathrm{^\circ C}$ I have to use ...
2
votes
0answers
40 views

Gibbs free energy of activation and activation energy [duplicate]

What the difference between Gibbs free energy of activation and activation energy
0
votes
0answers
32 views

Calculating melting temperature of water with thermodynamical data

So at zero degrees celsius($\pu{273 K}$), for clean water, we have the equilibrium eq.: $\ce{H2O(s) = H2O(l)}$ As it is at equilibrium, we know that $\Delta G = 0$. As we are dealing with clean ...
5
votes
2answers
63 views

Is temperature double-counted in the Gibbs free energy equation?

Complete amateur here. When looking at one form of the equation deriving the change in Gibbs free energy for a given chemical reaction, the terms change in enthalpy, and the negative product of ...
2
votes
1answer
44 views

Thermodynamics behind organic chemical reactions? [closed]

I took organic chemistry a few years ago at my university, and although I went through the motions to pass the exams, I didn't understand the thermodynamic reasoning behind why the reactions actually ...
1
vote
1answer
76 views

Why do we use external pressure when calculating work done by gas? [duplicate]

For irreversible expansion and compression, why is dw= -pextdV but not dw= -pdV ? Many of the texts and related questions on this site I encountered give a same general idea: because work done= ...
0
votes
1answer
49 views

Entropy and total differential

In an exercise, I have derived that $$\mathrm dS_\mathrm{m} = \frac{3R}{2T}\mathrm dT + \frac{R}{V}\mathrm dV$$ using the 1st and 2nd law of thermodynamics (1 mol ideal gas). Now, I want to write $\...
2
votes
0answers
55 views

Given Kd find equilibrium concentrations of the reactants

$$\ce{Biotin + Avidin → Complex}$$ Biotin is a vitamin derivative that binds extremely tightly to avidin (a protein found in egg white) with a $K_\mathrm{d}$ of $\pu{1e-15 M}$. If you make a ...
1
vote
0answers
16 views

Correct Generalization for Adair Equation?

I know how to derive the Adair Equation for n binding sites the long way, writing n+1 mini equations and linking them to relate all sub $K_b$ values to $K_{b-intrinsic}$. Tried to find a general ...
1
vote
2answers
64 views

Relation between ΔH and ΔE for the reaction in gaseous phase at constant temperature and pressure

Which of the following statements is correct for the reaction at constant temperature and pressure: $$\ce{CO(g) + \frac{1}{2}O_2(g) -> CO2(g)}$$ $\Delta H = \Delta E$ $\Delta H > \...
0
votes
0answers
45 views

Trying to understand rationale behind Joule-Thomson experiment

The purpose of the original Joule (as opposed to JT) expansion experiment was to assess intermolecular interactions in real gases. In that experiment, Joule immersed twin glass globes into a water ...
2
votes
1answer
79 views

Negative Molar Specific Heat of a Gas

It is known that the specific heat of a gas is process dependent. So it must be theoretically possible to have a negative value for a gas according to the following equation (for polytropic process, $...
3
votes
1answer
81 views

Current and reversible heat in battery reaction

In the book Battery Technology Handbook by Kiehne [1] (Google Books) on page 21, equation (32): The reversible heat effect per time unit can be related to current flow, because each multiple of the ...
3
votes
2answers
137 views

Energy balance in battery thermodynamics

I am trying to understand the derivation of a general energy balance in battery thermodynamics. The following relation is frequently found to determine the heat generation of a battery: $\dot{Q} = \...
3
votes
2answers
62 views

How to measure quantities at standard state when this state is a hypothetical one?

Consider the reaction $$\ce{A(g) + H2O(l) <=> B(aq) + C(g)}$$ If all gases and solutions were ideal, the standard state would be pure water, the solute B at a concentration of 1 M, the gases A ...