Skip to main content

New answers tagged

3 votes

Why does Entropy Increase on mixing two ideal liquids

If we have $1$ mol each of two different types of ideal gasses (He or Ne for example) at the same pressure and in two equal volumes separated by a partition if you remove the partition the gasses will ...
porphyrin's user avatar
  • 30.7k
3 votes
Accepted

Why does Entropy Increase on mixing two ideal liquids

Entropy is a measure of the number of ways (configurations) in which a system (the liquids before or after mixing) can be arranged subject to constraints such as the pressure and temperature. At the ...
Buck Thorn's user avatar
  • 22.4k
3 votes

Mathematical proof that more work is done in an isothermal than an adiabatic expansion?

As Poutnik states in the comments, since the integrand is the same, if we can prove that $p_\mathrm{isothermal}(V) > p_\mathrm{adiabatic}(V) \; \forall V$, that would be enough. Since pressure is ...
Metal Storm's user avatar
  • 3,476
3 votes

Mathematical proof that more work is done in an isothermal than an adiabatic expansion?

Let: $W_\mathrm{T}=\mathrm{isothermal\;work}$ $W_\mathrm{A}=\mathrm{adiabatic\;work}$ $y=\frac{W_\mathrm{T}}{W_\mathrm{A}}$ $x=\frac{V_\mathrm{o}}{V}$ $\lambda=\gamma-1$ Dividing both work expressions:...
Sam202's user avatar
  • 1,654
1 vote

Isobaric expansion vs Isobaric Free Expansion

If the volume of gas increases, but pressure stays the same, then something must be steadily supplying heat. PV = nRT yields T = PV/nR If P stays the same, and V increases, so must T. This is ...
DrMoishe Pippik's user avatar
0 votes
Accepted

Finding the point where reaction switches from endothermic to exothermic

Basically the slope of the adiabatic curve would satisfy the slope of the PV diagram, at a point where the curve and the PV line intersect (The PV line becomes tangent to the adiabatic curve). Based ...
Ronith's user avatar
  • 1,339
0 votes

Finding the point where reaction switches from endothermic to exothermic

From the first law of thermodynamics, $$dU=dQ-dW$$ The process goes form endothermic to exothermic when dQ=0. This is also tangent to some adiabatic reversible curve for the gas.
Chet Miller's user avatar
  • 13.5k
4 votes

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

It would be bad if you set the enthalpy of formation for both diamond and graphite to zero because one can react to form the other (and the enthalpy of reaction is non-zero). However, it is fine to ...
Karsten's user avatar
  • 40.7k
2 votes
Accepted

Closest attempt to making a Carnot Engine

The real life inefficiency of the Carnot cycle has nothing to do with nonideality of the system elements or their frictional losses or other dissipative issues. The real life efficiency problem with ...
hyportnex's user avatar
  • 557
0 votes

Equation of state for gas and liquid

I think i found the reason. Peng-Robinson is very steep and inaccurate at the gas-liquid boundary and even the smallest change in volume leads to enormous changes in pressure. The error could be as ...
Mariner's user avatar
  • 11
0 votes

Enthalpy of reaction with equal amounts of gaseous products and reactants

For an irreversible, complete reaction of the form: $$\ce{aA +bB->cC +dD}$$ The standard molar change in enthalpy is given by: $$\Delta\overline{H}^o=c\;\Delta\overline{H}_{f_C}^o\;+\;d\;\Delta\...
Sam202's user avatar
  • 1,654
4 votes
Accepted

Calculating the heat of reaction between sulfuric acid and sodium hydroxide

Arbitrary representation Species $\Delta H_f^o\;$ [kJ/mol] A $\ce{H2SO4(aq)}$ -909.27 B $\ce{NaOH(aq)}$ -469.15 C $\ce{Na2SO4(aq)}$ -1387.10 D $\ce{H2O(l)}$ -285.83 The reaction we have is: $$\ce{...
Sam202's user avatar
  • 1,654
5 votes

Author claims that for an ideal gas dU/dV=0

The internal energy depends on the random kinetic energy and the potential energy of interaction of the molecules. The latter is equal to zero when the specific volume is very high and the molecules ...
Chet Miller's user avatar
  • 13.5k
18 votes

Author claims that for an ideal gas dU/dV=0

The main idea is to obtain a mathematical expression only involving the measurable variables $p$, $T$, and $V$. We start with the internal energy as a function of its canonical variables. ...
Metal Storm's user avatar
  • 3,476
1 vote

Enthalpy change with uncertainties

source: https://www.chegg.com/homework-help/questions-and-answers/uncertainty-propagation-addition-subtraction-assume-use-ruler-shown-previous-questions-mea-q65974554 Refer to the formula sheet from ...
Ronith's user avatar
  • 1,339
0 votes

Gibbs energy of an imperfect crystal

I think you have a good understanding of the matter because what you say is correct. You might find the paper by Mosquera-Lois et al. [1] interesting where they go deeper in this balancing between ...
willempie's user avatar
0 votes

Why do we have water vapor at room temperature and atmospheric pressure when water is a compressed liquid at these conditions?

Why do we have water vapor at room temperature and atmospheric pressure when water is a compressed liquid at these conditions? If we kept vapor partial pressure below saturated vapor pressure, we ...
Poutnik's user avatar
  • 42.3k
0 votes
Accepted

Why do we have water vapor at room temperature and atmospheric pressure when water is a compressed liquid at these conditions?

I think that it is a good question: if you have ice in liquid water, even at 1°C (just above the melting point), all the ice will disappear and you will have 100% liquid. Then why do you have always ...
Guillaume's user avatar
  • 349
1 vote

Why do we have water vapor at room temperature and atmospheric pressure when water is a compressed liquid at these conditions?

Think of molecules of water liquid escaping into vapor, and molecules of water vapor condensing into liquid. Both processes occur simultaneously, and an equilibrium is reached in a closed system. The ...
DrMoishe Pippik's user avatar
0 votes

Two different approaches for calculating enthalpy change for methane + HCl

The first formula is only used to calculate the difference in energies of the reactants and products, so for this you have your endothermic and exothermic graphs to determine $\Delta{H}$. The second ...
DialFrost's user avatar
  • 315
1 vote

Will the total equilibrium pressure increase in gas phase reaction PCl5(g) ⇌ PCl3(g) + Cl2(g) after chlorine is removed?

After giving this problem more thought, I have come up with a better demonstration for why equilibrium pressure will decrease after removing the chlorine gas. Let: A = $\ce{PCl5}$ C = $\ce{PCl3}$ D = $...
Sam202's user avatar
  • 1,654
0 votes

Chemical reaction that can produce lots of heat from 2-3 simple liquid ingredients?

You do not state the end purpose of this quest. If you simply want to turn heat into electricity at a controlled temperature the source of heat is not relevant. If the purpose is to find a chemical ...
jimchmst's user avatar
  • 2,179
1 vote

The correct way of formulating change in enthalpy

Algebraically,$$P_2V_2-P_1V_1=\left(\frac{P_2+P_1}{2}\right)(V_2-V_1)+\left(\frac{V_2+V_1}{2}\right)(P_2-P_1)$$So, in your equation, you should be using the arithmetic average pressure and arithmetic ...
Chet Miller's user avatar
  • 13.5k
2 votes
Accepted

The correct way of formulating change in enthalpy

Note that $$\text{d}(pV)=p.\text{d}V + V.\text{d}p, \tag{1}$$ but \begin{align} \Delta(pV) &= p_2V_2 - p_1V_1 \\ &\ne p \cdot \Delta V + V \cdot \Delta p\tag{2} \end{align} \begin{align} \...
Poutnik's user avatar
  • 42.3k

Top 50 recent answers are included