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

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2
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1answer
28 views

Magnetic stirrer with hot plate

I did not know there are products such as a magnetic stirrer with a hot plate, enabling one to apply heat and stirring to a solution with relative ease. Did I understand correctly, that device needs a ...
7
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3answers
1k views

Temperature of an atom

I read somewhere that the temperature of an atom is not defined. The definition of temperature is only for larger systems. Why is this so?
3
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1answer
29 views

What is an example of a very low temperature endothermic reaction?

Shakashiri describes the reaction of solid Ammonium Thiocyanate and solid Barium Hydroxide Octahydrate resulting in an endothermic reaction leading to subzero temperatures. I've performed this ...
4
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1answer
52 views

Gibbs Free Energy : What is it trying to say actually?

"Gibbs Energy is the useful work that can be extracted from the heat of a rxn or a thermodynamic process." I understand how it predicts the feasibility of a chemical rxn, considering the Entropy ...
2
votes
1answer
33 views

How to calculate the heat capacity of a calorimeter?

I need to find the heat lost of an unknown metal dropped into a calorimeter with $70~\mathrm{g}$ $\ce{H2O}$. The initial temperature and final temperature of the $70~\mathrm{g}$ $\ce{H2O}$ and the ...
2
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2answers
50 views

Vacuum good inside a box?

I have no clue whatsoever about Chemistry on a academic point of view. We wish to transport some goods. Let's say we vacuum some of those goods, by doing like so: We place those goods on a box, we ...
3
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1answer
54 views

Reversible thermodynamic machine

Assume two identical solid blocks of copper with molar heat capacity at constant volume $C_{V,m}=24.5 \text{ J$\cdot$K$^{-1}$mol$^{-1}$}$ . Assume the heat capacity to be constant in the ...
2
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1answer
20 views

Good choice for heat-conductive coil submerged in sea water

I know only as much about chemistry as I can remember from a year in college. So, please speak slowly and use short words. I'm trying to decide on an appropriate material for a heat-transfer coil ...
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2answers
38 views

Gibbs energy and Entropy

In Gibbs energy equation- $\Delta G= \Delta H - T \Delta S$ At constant pressure, $Q=\Delta H$ (1) and we know that $T \Delta S = Q$ (reversible) so finally $T \Delta S=Q$ (2) Putting values ...
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2answers
32 views

What's sulphur's state of aggregation in petroleum?

Using google, I wasn't able to find an answer to this question. Conditions: p = 1 bar and T = 298 K.
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1answer
39 views

Why does the Born equation give the Gibbs free energy of solvation rather than enthalpy of solvation?

The Born equation gives the difference in energy required to charge a particle in a vacuum and in solution which results in the work required to transfer an ion from a vacuum into solution. It is ...
0
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1answer
37 views

What happens to energy changes in non-reversible processes?

Take internal energy for example: $$dU\leq TdS-PdV$$ Firstly, I would like to make clear that the following question/argument relies on the following statement being correct: the left hand side of the ...
2
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3answers
59 views

For a system to undergo a spontaneous change at constant temperature and pressure the Gibbs free energy must decrease, but how?

$$dG<VdP-SdT$$ So for a process at a constant pressure and temperature, and in the absence of any non-pV work, $dG<0$. Since energy cannot be created or destroyed (and Gibbs free energy is a ...
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0answers
13 views

Are the values for enthalpy, internal energy and Gibbs free energy the same for a particular process?

Internal energy, enthalpy and Gibbs free energy are all units of energy. So, for any particular process where energy is lost from the system the same amount is given off to the surroundings. Am I ...
7
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3answers
346 views

Whats the difference between entropy and the (dis)order of a system?

Entropy is often verbally described as the order/disorder of the thermodynamic system. However, I've been told that this description is a vague "hand-waving" attempt at describing what entropy is. For ...
2
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1answer
34 views

How does the chemical potential allow for open systems to be considered?

Gibbs free energy can be defined as: $$dG=VdP-SdT+\sum_i\mu_idn_i$$ where $\mu=(\frac{\partial G}{\partial n})_{P,T}$. Last term, $\sum_i\mu_idn_i$ allows for open systems to be considered (where $dn$ ...
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1answer
45 views

Gibbs free energy can be expressed as a function of P,T and n but are enthalpy and internal energy also (partially) functions of n?

$$G=G(P,T,n)$$ $$dG=VdP-SdT+\mu dn=(\frac{\partial G}{\partial P})_{T,n}dP+(\frac{\partial G}{\partial T})_{P,n}dT+(\frac{\partial G}{\partial n})_{T,P}dn$$ This allows open systems to be considered ...
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0answers
30 views

Can state of matter from liquid to gas maintain the same molecular structure in PE or in polymers in general, like water does?

If I’ve got a reactor containing PE-Polyethylene $(\ce{{C2}$H_\text{4})n$}$ (solid) and the rest is filled with nitrogen gas. The system is closed. Supposing we have an initial temperature of ...
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1answer
37 views

If the standard state symbol means that the substance is pure (and at 1 bar) how is it possible to have a standard REACTION enthalpy?

For the reaction one mole of substance $A$ in equilibrium with one mole of substance $B$ the standard reaction enthalpy is defined: $$\triangle_rH^{\theta}(T)=H_m^{\theta}(B;T)-H_m^{\theta}(A;T)$$ ...
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2answers
29 views

Why is dG=dH-TdS?

I get that $G=H-TS$ because then: $dG=dH-TdS-SdT=TdS+VdP-TdS-SdT$. Therefore, by cancelling: $dG=VdP-SdT$ which is the equations for dG. However, I cant get this result from using $dG=dH-TdS$. ...
2
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1answer
34 views

Problem with proving that entropy is a state function

$$dU=dq-pdV$$ $$dU=C_VdT$$ Side question: is the above equation, $dU=C_VdT$ true only for a perfect gas or all substances? $$C_VdT=dq-pdV$$ $$dq=C_VdT+pdV$$ Divide by T $$dS=\frac{C_V}{T}dT+\frac ...
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0answers
17 views

Thermodynamic micellization of potassium N-dodecanoyl-DL-serinate via conductivitiy measurements

I have a set of data and my instructor asked me to calculate some parameters but I am not good in maths. I will give you for data potassium N-dodecanoyl-DL-serinate (DL-KDDS); K: Conductivity C: ...
5
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1answer
70 views

Why is Gibbs free energy more useful than internal energy?

$$\mathrm{d}U<T\,\mathrm{d}S-p\,\mathrm{d}V= \left(\frac{\partial U}{\partial S}\right)_{\!V}\,\mathrm{d}S +\left(\frac{\partial U}{\partial V}\right)_{\!S}\,\mathrm{d}V$$ So for a change to occur ...
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1answer
22 views

Can a change in internal energy always be expressed as the product of the constant volume heat capacity and the change in temperature?

It makes sense to me conceptually that $dU=C_VdT$ but is that always the case because I have seen that result derived thus: $$dU=U(V,T)=(\frac{\partial U}{\partial T})_VdT+(\frac{\partial U}{\partial ...
2
votes
1answer
52 views

Calculating the Gibbs Free Energy of Mixing

This is a Physical Chemistry Question and comes from the Atkins Physical Chemistry book. The answers are given but I don't understand how to get to $-9.7~\mathrm{kJ}$ for the first part of the ...
4
votes
2answers
28 views

Expressions for constant volume and constant pressure heat capacities

My lecture handout says: $$C_V=\frac{dq_V}{dT}=(\frac{\partial U}{\partial T})_V$$ I understand that $C_V=\frac{dq_V}{dT}$ and that $dU=dq_V$ but what's the need for the partial derivative. Why can ...
0
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1answer
38 views

Why do heavier elements have smaller specific heat values.

In the periodic table the trend is that as the mass of each element increase's the specific heat tends to go down. This seems to be counter-intuitive because if I am not mistaken as mass increase's ...
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2answers
51 views

Which formula is correct for calculating the heat of dissolution?

I want to calculate the energy change when a solute is dissolved in water. I know that I can achieve this by using the equation $q=mc \Delta T$. My question is does the mass ($m$) change with the ...
3
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1answer
96 views

How to determine the molar enthalpy of hydration of sodium sulfate in the laboratory?

There are two separate experiments done in this problem. First experiment 106.6 gram of water at 23.28 C and 8.56 gram of sodium sulfate places into a foam cup (a calorimeter) the temperature to ...
2
votes
1answer
56 views

How to find and use the Clausius-Clapeyron equation

I know how to get the equation from the Clapeyron equation but I have a question regarding a the integration along a phase boundary and a small step in the derivation that I will make clear when I ...
0
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1answer
26 views

The reaction of Nitrogen trichloride explosion is 2NCl3(l) -> N2(g) +3Cl2(g); which of the graphs represents this reaction?

This is a homework question and I'm finding it hard to understand, so an explanation why will be great. Image of graphs a, b, c, d Thanks!
2
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1answer
40 views

Does the density of a liquid and gas phase of a substance(nitrogen or water) converge when reaching critical point

I know that the there is no difference in density in a liquid and a gas phase of a substance after the critical point. But I do want to know if this difference in density is more continuous or if it ...
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2answers
354 views

Why is dU an exact differential and dq an inexact differential?

dU, dG, dH etc are all exact differentials and the variables themselves are known as state functions because they only depend on the state of the system. However, dq and dw for example, are inexact ...
2
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2answers
92 views

What happens when an explosion can't lead to volume increase of the thermodynamic system?

I have been searching for an answer to the question for a while but was not able to find 1. My question is: What if an explosion is not able to exit the container?-... so lets take a pipe bomb for ...
3
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2answers
107 views

A misunderstanding about the energy profile of reactions with a catalyst involved

All of us are aware of the importance of the catalysts in bio-chemistry. For a high school learner like me, catalysts ,and therefore, enzymes play a bridge-like role that connect high school bio to ...
2
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0answers
31 views

Ratio of MbO2/Mb in a satured solution of dissolved oxygen from dry air

What is the ratio of $\ce{MbO2/Mb}$ if the solution is saturated with air? Details of the question: \begin{align} &&\ce{Mb + O2 (aq) &-> MbO2}\\ &&\Delta G' &= ...
1
vote
1answer
21 views

Why is a reaction more favorable if one of the products is not soluble/sparingly soluble?

I have heard people go so far as to say that the "driving force" of a reaction is the formation of the precipitate. Why is this so? Whilst the process is almost certainly exothermic (I think - please ...
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0answers
20 views

Chemical Thermodynamics

In this pic, you can see the report for lab work. I did the labwork, and it is asking -to find delta H pr -? -delta H (theor)-? -error ? Please help me to find those
3
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1answer
40 views

Why is it necessary to consider infinitesimal changes in p,V,T for H,U and G given that they're state functions?

State functions such as $G$ only depend on the state of the system and are not dependent on the "path" that took the system to that state (which would be the case for work, for example, which is not a ...
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2answers
73 views

Why does N2 react with O2 to Form NO at high temperatures?

This also raises questions that I have about the Haber Process which produces ammonia ($\ce{NH3}$) from molecular nitrogen ($\ce{N2}$) and hydrogen ($\ce{H2}$). I have heard multiple times that bond ...
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0answers
19 views

Finding the thermodynamics of protein unfolding from temperature and absorbance using fluorescence spectroscopy?

I recently did an experiment on protein unfolding using a Perkin Elmer fluorescence spectrometer. The protein was $\alpha$-chymotrypsin. I was given this paper for my procedure. I am now trying to ...
3
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1answer
35 views

How to derive the pressure dependency for the Gibbs free energy?

$$\mathrm{d}G=\left(\frac {\partial G}{\partial p}\right)_T+\left(\frac {\partial G}{\partial T}\right)_p$$ The above is an exact differential. Firstly what does this mean physically? (I hear about ...
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1answer
39 views

Thermochemistry problems?

Question 1: A compound A reacts according to the following hypothetical equation and has a molecular weight of 48.36 g/mol. 3 A (s) +B (aq) ––> 2 C (aq) ∆H° = ? A sample of A, weighing 0.152 g ...
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1answer
40 views

How to calculate the activation energy of diffusion of carbon in iron?

At room temperature, $298~\mathrm{K}$, the diffusivity of carbon in iron is $9.06\cdot 10^{-26}\frac{m^2}{s}$. At $573~\mathrm{K}$ the diffusivity is $1.66\cdot 10^{-15}\frac{m^2}{s}$. What is ...
4
votes
1answer
58 views

Phase diagrams (weird region)

On the left, there is a region for $\ce{MgO(ss)}$. I've been told such regions exist because stuff are not miscible. However, does that mean the composition axis on the bottom is a lie? Namely, ...
7
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1answer
327 views

What Causes there to be a Maximum Amount of Salt which can be Dissolved in Water?

When you add salt to water and stir, after a while the salt will no longer dissolve. Why is this?
4
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1answer
82 views

Do water hybrid cars really exist?

I have heard a few claims about water-fueled cars. Being a student of Engineering I totally understand that water-fueled cars (using electrolysis to generate Hydrogen) are nothing more than a hoax, ...
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vote
1answer
21 views

What will happen to the entropy and free energy of the gasses when the partition is removed?

Consider a container of volume $ 5.0$ L that is divided into two compartments of equal size. In the left compartment there is nitrogen at $1.0$ $atm$ and $25 °C$; in the right ...
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1answer
55 views

Where does this equation for the activity in the gas phase equilibrium between N2, H2 and NH3 come from?

I have a question with Equilibrium Constant. I understand that for a reaction in equilibrium $aA +bB \rightleftharpoons cC +dD$ $$K_c= \frac{[C]^c[D]^d}{[A]^a[B]^b}$$ and $K_p$ is just using the ...
16
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4answers
4k views

Hypothetical: What happens to water as pressure increases to infinity?

I've asked a similar question here but the answer given shows the behaviour of water under general conditions. I'd like to know what the behaviour of water is like as pressures increase towards ...