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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2answers
70 views

Which substances have the highest/lowest enthalpy of formation per gram?

Which substances have the most extreme enthalpies of formation per gram at standard temperature and pressure?
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24 views

Thermal conductivity and enthalphy data for nitrogen gas

I am struggling to find the data for thermal conductivity and ethalphy of nitrogen gas at reduced pressure (500 mbar). Most of the information is for nitrogen gas at 1 bar or above. Does anyone know ...
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2answers
67 views

Is heating water endothermic?

So I got a problem recently which asked to calculate the amount of energy needed to increase the temperature of 200 g of water from 26 to 51 degrees Celsius. The value I got was 20900 J. So far I ...
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2answers
73 views

Is Gibbs energy change during osmosis positive? If so then why is it spontaneous?

For ideal solution, μA=μA* +RT lnxA ln function is an increasing function, means that the higher the xA the higher the μA......(1) Now consider osmosis. From Atkins' Physical Chemistry Ninth ...
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0answers
28 views

Calculate chemical potentials to find electrode Fermi level

I'm running some simple simulations of the semiconductor-electrolyte interface and I'm having a hard time figuring out the equilibrium condition. Can someone please help me with my electrochemical ...
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0answers
15 views

Why a Differential Scanning Calorimeter (DSC), to measure thermodynamic parameters, has problems?

I want to use a Differential Scanning Calorimeter (DSC) to determine when my protein unfolds as you increase the temperature in a DSC machine. The machine is pressurised (to 3A) during the run, so ...
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2answers
58 views

For Hess' law type questions, when do you take the inverse of the constant and when do you switch the sign?

For example, when you're given the enthalpy $\Delta H$ of a reaction and you want to switch that reaction around in order to add it to something else, you switch the sign. Furthermore, when adding ...
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2answers
49 views

Why enthalpy of adsorption is negative?

I have already read Is adsorption exothermic, and if so, why? but it didn't answered my query. To illustrate, let's take a hypothetical vacuum space. In that space, there is a solid and a gas, the ...
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1answer
182 views

What is the Gibbs energy of dissolving a solid in pure water?

I am calculating the Gibbs energy of dissolving one mole of solid glucose in pure water such that the final solution has a volume of one liter and a concentration of one mole per liter. I have three ...
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1answer
77 views

Mixture of water, methanol and dichloromethane

If I have a mixture of 25 vol% methanol in water and I mix it with an equal volume of dichloromethane (which is miscible with methanol but not water) can I roughly say that both phases (i.e. water and ...
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1answer
57 views

Is temperature of crystallisation same as melting point temperature for polymers?

Melting point tends to be a temperature range. Is it true that the temperature of crystallisation is the highest temperature at which the polymer melts and thus there is some distinction between ...
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1answer
114 views

Heat of formation of aqueous H⁺

In my book it is given that by convention heat of formation of aqueous $\ce{H+}$ is taken to be zero. Heat of formation is energy released or absorbed when 1 mole of a compound is formed from its ...
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4answers
106 views

How does the room gets heated by leaving a fridge open?

Question: If the door of the refrigerator is kept open, the room in which the refrigerator is kept: gets cooled gets heated neither gets cooled nor gets heated gets cooled or heated ...
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122 views

Derivation of Gibbs free energy formula

Okay, so I'm trying to derive an important formula which states that - ∆G(r) = ∆G° + RTln( RQ ) where ∆G(r) is the instantaneous rate of change of Gibbs energy with ...
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Why is high pressure and high temperature favourable for the formation of diamond? [duplicate]

Graphite can be converted to diamond and this conversion is favourable under high pressure and high temperature. Is there a reason for this from the point of view of "Le Chatelier's Principle"? I ...
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135 views

What is the ideal temperature and pressure to crack water?

Using sun mirrors and solar cells for electricity. What temperature, pressure and voltage ideal for cracking water. Source: NPR Source Would it take more or less electricity to crack water under ...
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1answer
360 views

Calculating entropy change: reversible vs irreversible process

Since the change in internal energy and enthalpy, which are equal to the heats for a constant-volume and constant-pressure process, respectively, are state functions, the heats for a reversible v.s. ...
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4answers
136 views

Is heat just a change in temperature?

According to my chemistry textbook, heat is defined as "Energy that is exchanged because of a difference in temperature or a change in phase." My textbook also says, "Heat is a form of energy. ...
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20 views

What are the activation energies for the combustion of RP-1 with liquid oxygen, and UDMH with Dinitrogen tetroxide?

I need to compare the chemical and physical properties of the two reactions for a school project. However, I can't find a source that explicitly states their activation energies! We haven't learned ...
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27 views

Regarding ΔG and equilibrium constant [duplicate]

We know that $$ΔG = ΔG^\circ + RT\ln{Q} \tag{1}$$ where $Q$ is reaction quotient, and also that at equilibrium becomes $$ΔG^\circ = -RT\ln{k} \tag{2}$$ I was trying to apply this equation to a ...
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1answer
90 views

Intensive and Extensive Properties--Resistance

Is resistance an intensive quantity or an extensive one? And why? Let me present 2 scenarios. Resistance of a wire: The resistance of a wire depends on area and length. This implies it depends on the ...
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68 views

Whether the entropy change of the system is positive or negative

$$\ce{N2(g) + O2(g) → 2NO(g)}$$ My thinking: since gases are combined together, so there randomness or disorder gets decreased. Hence the sign of entropy change of the system should be negative. ...
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2answers
87 views

Question about liquid-phase in P-T Diagram

Currently, I have been learning about P-T diagrams and vapour pressure and I have a question that seems like it should have a simple explanation yet I am not able to understand it. Taking the P-T ...
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2answers
510 views

Gibbs Free energy of a reversible reaction

From what I understand, it sounds like the Gibbs Free Energy change of a reversible reaction at equilibrium is zero. However, since I know that Gibbs Free energy change depends on temperature, does ...
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0answers
118 views

Conversion of graphite into diamond [duplicate]

The standard state Gibbs free energies of formation of C(graphite) and C(diamond) at $T = \pu{298 K}$ are $\pu{0 kJ mol-1}$ and $\pu{2.9 kJ mol-1}$, respectively. The conversion of graphite [C(...
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2answers
127 views

Can an exothermic (endothermic) process increase (decrease) internal energy?

We classify exothermic and endothermic processes based on enthalpy change, $\Delta H < 0$ and $\Delta H > 0$ respectively. I assume this translates to $\Delta U < 0$ and $\Delta U > 0$, ...
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2answers
397 views

What is a good source for large tables on the properties of water?

I'm currently doing an investigation for school on finding the Clausius-Clapeyron relation/gradient for boiling water and comparing it to the gradients along my line of best fit. It is given by the ...
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1answer
177 views

Are the vibrational modes of CO2 active at room temperature?

I was doing an experiment whereby I had to measure the specific heat ratios of certain gases. Carbon dioxide came out to be around 1.3, and checking with the accepted values this is close. My question ...
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1answer
93 views

Behavior beyond the critical pressure [closed]

I have seen some phase diagrams that look like this: https://www.learner.org/courses/chemistry/images/text_img/phase_diagram_water.jpg And also some like this: https://en.wikipedia.org/wiki/...
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63 views

AP Chem Question about Reaction Rate - Confused?

I found this question in the AP Chem book, and I understand why B is the answer (as the answer key says). However, I don't understand why D is not also correct. The question is: A multistep reaction ...
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1answer
40 views

Why do reactions happen at all? [closed]

What makes some atoms/compounds reactive and some noble? What is the fundamental truth behind a reaction? It seems that two species can undergo number of combination to give a compound. Say Sodium and ...
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2answers
206 views

What will be the sign of work done?

Consider the following question: The enthalpy of vapour is $10\ \mathrm{kcal}/\mathrm{mol}$ higher than liquid at $350\ \mathrm{K}$ and $2\ \mathrm{atm}$. Under given conditions, the difference ...
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2answers
86 views

Does the reaction become more or less favorable as temperature increases?

Suppose a reaction has $\Delta S > 0$ and $\Delta H < 0$. The equation $\Delta G = \Delta H - T\Delta S$ predicts that as the temperature increases, the reaction becomes more favorable because ...
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2answers
80 views

Why is heat capacity defined as a partial derivative?

I understand that the heat capacity is the gradient of the slope of q against T, which implies that C = $\mathrm{ \frac{dq}{dT}}$, so how do we arrive at C = $\mathrm{\frac{∂q}{∂T}}$? At constant ...
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1answer
82 views

Meaning of an ideal chemical system [closed]

What is meant by a an ideal chemical system? Moreover, is it true that only in an ideal chemical system the equation $$\mathrm{d}U = \mathrm{d}H - \mathrm{d}(pV),$$ i.e. $$\Delta U = \Delta H - \...
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1answer
45 views

What is p defined as for the expansion and compression of an ideal gas system in the equation ΔU = ΔH - pΔV?

$$\Delta U = \Delta H - p\,\Delta V$$ Consider a gaseous system in a container with a frictionless piston, and a pressure outside the container. Is the pressure outside the container assumed to ...
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2answers
462 views

Is the differential, dp, exact or not? [closed]

Consider the differential $$\mathrm dp=\frac RV\,\mathrm dT+\left(\frac{2a}{V^2}-\frac{RT}{V^2}\right)\,\mathrm dV$$ (where $a$ is a constant value) (a) Determine whether the above differential, ...
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2answers
154 views

Why is change in entropy negative and change in enthalpy negative for the reaction of Magnesium and Hydrochloric acid?

So $$\ce{Mg(s) + 2 HCl(aq) -> H2(g) + MgCl2(aq) + Heat}$$ From a conceptual standpoint, shouldn't the change in entropy be positive for this reaction because there are more moles of gas in the ...
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1answer
127 views

How does the proticity of an acid affect the enthalpy change of its reaction with a base?

For an experiment I've carried out a series of reactions between monoprotic bases (ammonia and potassium hydroxide) and several acids. Two of these acids were monoprotic (hydrochlori acid and ethanoic ...
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2answers
297 views

Derivation of work done by real gas

According to the Wikipedia on real gases, it is stated that the expansion work done by a real gas differs from the ideal gas by $\int\left(V-\frac{RT}p\right)\,\mathrm dp$. Firstly, does this mean $...
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1answer
77 views

Is ΔV in ΔU = ΔH - pΔV always a positive number? [closed]

I know that $ΔU$ and $ΔH$ can be both positive and negative, but what about $ΔV$? I presume $ΔV$ can be both positive and negative as $w=-pΔV$, pressure always positive, and $w$ can be positive or ...
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1answer
89 views

How does refrigerator actually work?

In refrigerator, heat energy got extracted from cold sink and dumped into hot source. This is not spontaneous so work must be done. I came across the following while reading a textbook: For ...
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2answers
244 views

Calculating the strength of an ionic bond that contains poly-atomic ions

So the bond association enthalpy for ionic compounds like $\ce{NaCl}$ and $\ce{NaBr}$ can be easily calculated from a Born-Haber cycle. But the way a Born-Haber cycle is constructed it uses info that ...
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1answer
202 views

Find the minimum temperature at which the reaction will become spontaneous [closed]

This question came in my entrance exam and I think 273 K should be the answer because the reaction is already spontaneous. I just want to know if I've attempted it correctly. For a certain ...
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1answer
317 views

Pressure at which graphite and diamond are in equilibrium

I came across this problem : The standard state Gibbs free energies of formation of C(graphite) and C(diamond) at $T = \pu{298 K}$ are $\pu{0 kJ mol-1}$ and $\pu{2.9 kJ mol-1}$, respectively. ...
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0answers
22 views

Is there a website or book that contains accepted values for the enthalpy change of the reactions between acids and bases?

I am looking for a website/book/journal/etc. which contains the accepted values for the enthalpy change of the follwoing reactions: Hydrochloric acid with potassium hydroxide Hydrochloric acid with ...
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1answer
233 views

Effect of temperature on equilibrium constant in terms of entropy change

This question was asked in the JEE examination of 2017 : [A] option is incorrect since the system is losing heat and hence $$ \Delta S = -ve$$ [B] Lets assume we have an endothermic reaction $$\...
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1answer
56 views

Simple alternative to UNIFAC to prove that a mixture containing 1ml of x and 5 litres of propylene glycol is not flammable?

Section 2.6.1 of the REGULATION (EC) No 1272/2008 (CLP) defines a flammable liquid as: Flammable liquid means a liquid having a flash point of not more than $60 ^{\circ}$C. So data on flash ...
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3answers
131 views

Estimating the absolute entropy of water at room temperature

I thought it would be fun to get an idea of how enormously large $W$ in $S = k\ln W$ is. I'd specifically like to estimate this for a mole of water at $\pu{1 atm}$ and $\pu{298 K}$. To do this, I ...
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2answers
686 views

Entropy change of isothermal irreversible expansion of ideal gas [duplicate]

Two mole of an ideal gas is subjected to isothermal expansion from $\pu{2 atm}$ to $\pu{1 atm}$ at $\pu{300 K}$. Calculate entropy change of the system, surrounding and total, if the process is ...