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

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Negative and Zero Enthalpy?

I've been investigating chemical kinetics and stumbled across the CHEMKIN program manuals and the JANAF tables. In the original CHEMKIN database they list 'standard enthalpy'. I've checked and this is ...
0
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26 views

Unknown Mass in Dalton's Law of Partial Pressures

An air with mass of 0.454kg and an unknown mass of CO2 occupy an 85 Liters tank at 2068.44 KPaa . If the partial pressure of the CO2 is 344.74 kPaa, determine its mass. Answer is 0.138kg Ok lets ...
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1answer
18 views

Temperature Dependent Specific Heat of Nitrogen

Calculate the change in enthalpy as 1kg of nitrogen is heated from 1000K to 1500K, assuming the nitrogen is an ideal gas at a constant pressure. The tempreature dependent specific heat of nitrogen is ...
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8 views

Expressions that relate to a particular gaseous mass

The following expressions relate to a particular gaseous mass: PV = 95T, h = 120 + 0.60T where these units obtain in psf, V in ft^3/lb, T in Rankine and h in Btu/ln. If th specific heats are ...
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22 views

How can I use sunlight to heat a RBF and reflux a reaction?

This may seem like a off topic question but I really need help on it. I am currently working on a polymerization reaction in which I'm breaking down plastic polymers into smaller molecules. However, ...
5
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1answer
58 views

Average or individual molar heat capacity?

In finding enthalpy change $\Delta H$ during adiabatic, reversible expansion of mixture of two ideal gases $n_1$ mol of $\ce{A}$ ($C_{\mathrm{m},v}=\frac{3}{2}R$) and $n_2$ mol of $\ce{B}$ ...
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1answer
42 views

Ideal gas in a box and leaked out in vacuum [closed]

an ideal gas is at pressure $P$ and temperature $T$ in a box,which is kept in vacuum with in a large container. the wall of the box is punctured .what happens to temperature as the gas occupy entire ...
4
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1answer
72 views

Cis-trans isomers internal energy

Whilst reading about stereochemistry, I came to know that the stability and melting point of cis isomers is lower than trans isomers. By searching on net I've found the reason behind that. But one ...
3
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1answer
63 views

Fundamental equation of thermodynamics for magnetocaloric materials

The fundamental equation of thermodynamics, as us chemists (and chemical engineers!) are used to seeing it, is $$ dG = - S~dT + V~dP + \sum_{i}\mu_i~dN_i$$ This gives the Gibbs free energy as a ...
4
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1answer
41 views

Why is change in gibbs energy not zero through the gibbs free energy equation?

Change in enthalpy of the system is equal to its temprature multiplied by its change in entropy (as change in enthalpy is equal to heat absorbed /given out at constant pressure and change in entropy ...
6
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76 views

Temperatures Below Absolute Zero

This seems like a farce... http://www.nature.com/news/quantum-gas-goes-below-absolute-zero-1.12146 I have seen several recent articles like this one and I am extremely skeptical. Perhaps my ...
3
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1answer
30 views

Virial equation of state - Taylor expansion

I don't get how Taylor expansion over $ \frac{1}{\overline{V}} $ of Virial equation of state is caried out: $Z = \frac{P\overline{V}}{RT} $ which yields $$ Z = 1 + \frac{B_{2V}(T)}{\overline{V}} + ...
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1answer
58 views

Which temprature is taken in Gibbs free energy equation, of the system or the surrounding? [duplicate]

Which temprature is taken, the temprature of the system or the temprature of the surrounding? I think it should be the temprature of the surrounding. This is because if we take the temprature of the ...
5
votes
1answer
81 views

Specific heat capacity question - mass of iron needed to melt ice and raise temperature of water?

My answer was that you needed 25041.67J to melt the ice and 16108.4J to raise the temperature to 22 degrees. Therefore $mc \Delta T(iron)$ = -(25041.67 + 16108.4) and dividing this by the mass of ...
3
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1answer
80 views

Can someone explain the equation for entropy?

Here's the equation: $\Delta S = \frac{\Delta q}{T}$ The confusion I have with this equation lies in the variable for temperature, $T$. Why is the temperature constant in this equation? Why can't ...
3
votes
1answer
74 views

How to distribute the Boltzmann energy to internal and external motion?

If we have an isolated pentane molecule at room temperature (RT) the Boltzmann energy $(E=k_\mathrm{B}T)$ is approxately $0.59\ \mathrm{kcal/mol} \overset{\wedge}{=} 207\ \mathrm{cm^{−1}}$. There is ...
2
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1answer
40 views

Why is lithium bromide used in absorption refrigerators?

Lithium bromide refrigerator Why is lithium bromide used in absorption refrigerators? It is more expensive than sodium chloride. The wikipedia article on lithium bromide says it is extremely ...
3
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1answer
18 views

How does Ammonia and water mixture works in an absorption refrigeration?

As per one of the questions in this site $$\ce{NH3 + H2O -> NH4 + OH}$$ However, per another perspective in absorption refrigeration The mixture is placed in the same container. Then when it ...
6
votes
2answers
211 views

How can I figure out whether a reaction is endothermic or exothermic without its enthalpy value?

I already know the way to determine whether if the given reaction is exothermic or endothermic by the enthalpy values. But is it possible without enthalpy values, and just by looking at the reaction? ...
3
votes
1answer
32 views

Regarding Gibbs's function, why is there non-expansion work?

It has been defined as the energy available for work other than expansion work. Why can't it be used for expansion work? I think I'm missing something here
4
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1answer
83 views

Can the thermodynamic predictions of redox reactions based on E and dG contradict each other?

I am referring to the following three reactions. Two of these reactions are imaginary ($\ce{M}$ and $\ce{X}$ are imaginary). $$\begin{alignat}{3} \ce{X- + 2e- \;&<=> X^3-} \qquad ...
4
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2answers
441 views

On adding sugar to water, does the entropy increase or decrease?

This question is a little confusing. According to my teacher the entropy should decrease, but I think that sugar is crystalline first and later it dissolves, so the randomness increases and so the ...
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1answer
35 views

What are the possible changes that might occur if I add an inert gas to a chamber containing another few different gases?

As an example, let's assume that we have a gas $\ce{P(g)}$ inside a chamber and when the temperature inside it increases to a certain value there is an equilibrium that prevails inside the system. So ...
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1answer
59 views

Does the temperature of water affect its ability to extinguish fires?

Since water can be either hot or cold, does its temperature affect its ability to extinguish fires?
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37 views

When the heat is absorbed by the ice then ice will melt to form liquid water

My new try: Given data Energy given by reaction =1690 kJ Initial temperature = 0 oC Final temperature = 50 oC C water = 4.18 Jmol-1 K-1 ?Hfus ice = 6.01 kJ*mol-1 Calculate Mass of ice = ? Ice ...
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1answer
56 views

Lead compounds enthalpy homework

Consider the following: $\ce{PbS(s) + \frac{3}{2}O2(g) -> PbO(s) + SO2(g)}~~~\Delta H^\circ= -413.7~\mathrm{kJ}$ $\ce{PbO(s) + C(s) -> Pb(s) + CO(g)}~~~\Delta H^\circ = +106.8~\mathrm{kJ}$ a. ...
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1answer
50 views

Use bond enthalpies to estimate ΔH of reaction: [closed]

Use bond enthalpies to estimate $\Delta H$ of reaction: $\ce{HCl(g) + F2(g) -> HF(g) + ClF(g)}$ $\begin{alignat}{2} &\ce{HCl}\ &&431\ \mathrm{kJ/mol}\\ &\ce{F2}\ &&158\ ...
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27 views

Reaction-enthalpy for synthesis of 40 g hydrazine

Problem: Calculate the reaction-enthalpy for the synthesis of 40 g hydrazine (rocketfuel): $$\ce{4 NH_3 (g) + Cl_2 (g) -> N_2 H_4 (l) + 2 NH_4 Cl (s)}$$ Attempt at solution: First we have to ...
3
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1answer
41 views

Equilibrium constant in terms of partial pressures

$K_p$ is defined as $\Pi_j(\frac{P_j}{P^{\Theta}})^{\nu j}$ where $P_j$ is the partial pressure of component j and $\nu$ is the stoichiometric coefficient. I have a couple of questions already. ...
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1answer
60 views

How is it possible for a substance to have a high heat of vaporization but a low boiling point?

The final paragraph of Dissenter's question here is worthy of standing alone: [H]ow does one square a high heat of vaporization with a low boiling point? If it takes a lot of energy to vaporize ...
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37 views

Entropy change when liquids at two different temperatures are mixed

Two quantities of water ($M_\mathrm{r}=18$) each of mass $216\ \mathrm{g}$ are mixed together in a vessel. The temperatures of the two quantities before mixing are $303\ \mathrm{K}$ and $333\ ...
3
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2answers
274 views

Reversible process in thermodynamics

How can we look at reversible processes in an intuitive manner? How is it possible, that at any moment, it can be reversed by an infinitesimal change?
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44 views

How to find the standard enthalpy and entropy for the dissolution of silver chloride?

A maximum of $1.89~\mathrm{mg}$ of $\ce{AgCl}$ will dissolve in $1.00~\mathrm{L}$ of solution at $25.00~^\circ\mathrm{C}$. A maximum of $5.26~\mathrm{mg}$ of $\ce{AgCl}$ will dissolve in ...
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0answers
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What is the explanation of the odd even effect in liquid crystals?

What is the most accepted theory for explaining the odd even effect in liquid crystals? Can anyone explain and refer the corresponding paper?
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12 views

Melting temperature vs Isotropisation temperature in liquid crystals

What is exactly the difference between these two? I think melting point is when the compound melts down to visually liquid state but actually LC state and latter is when polymer becomes completely ...
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76 views

How different concentration of HCl on magnesium affect the enthalpy change

I had conducted an experiment where I reacted a $0.3\ \mathrm{g}$ strip of magnesium with $100\ \mathrm{mL}$ of varying concentrations of $\ce{HCl}$: $1\ \mathrm{mol/L}$, $2\ \mathrm{mol/L}$ and $3\ ...
6
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1answer
76 views

Thermodynamics of photochemical reactions

Suppose I have a photochemical reaction in gas phase, such as $$ \ce{CO2 + {$h\nu$} -> CO + O}. $$ I would like to work through the thermodynamics of such a reaction and understand the meaning of ...
6
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2answers
479 views

When I heat up a balloon, does the air inside increase in pressure as well as volume?

When I heat up a balloon, does the air inside the balloon increase in pressure as well as volume? I thought pressure and volume were inversely proportional? Or does pressure and volume increase as ...
1
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1answer
75 views

Entropy increase when heating a gas

What is the entropy change when the temperature of 1.00 mol of ideal gas is raised reversibly from 10 °C to 50 °C at constant pressure, constant volume, and assuming the heat capacity is independent ...
4
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0answers
64 views

Is helium-4 a liquid at zero temperature and zero pressure?

As far as I know, for all substances other than helium, if you extrapolate the solid-gas line on the phase diagram, it passes through the origin. That is, no matter how low the temperature is, you can ...
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1answer
61 views

Heat and water absorption by calcium chloride

Can calcium chloride be effectively used as a desiccant to absorb both heat and moisture?
5
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1answer
129 views

Vaporized sodium hydroxide?

Some time ago, I was making a $\ce{NaOH}$ solution. The solution I had made was much too concentrated, and the heat released in the dissolution of the ions caused the water to begin steaming. ...
0
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1answer
39 views

Equations for internal energy and their relevance to the derivation of the equation for entropy for perfect gases

My lecture handout proves derives an expression for entropy thus: For a perfect gas $U=U(T)$ (i.e. is not dependent on volume; only temperature). Therefore, $(\frac{\partial U}{\partial V})_T=0$ ...
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1answer
53 views

Is hot air or hot water more effective at melting a frozen pipe?

This question is related to specific heat, and I thought I understood it but I've managed to confuse myself. My initial reasoning was that since in both cases, the pipe is the same, the amount of ...
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4answers
282 views

What is the origin of the maximum in rotational heat capacity?

The graph of rotational heat capacity above shows a small maximum before approaching the equipartition value. What is the origin/physical explanation of this maximum?
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1answer
67 views

In order to solve for this equation for heat capacity, do I need to treat it as a system of equations?

For a lab, we took the temperature of 15ml of tap water, $q_{cool}$, then added 20ml of tap water warmed to 80 degrees Celsius, $q_{warm}$. We recorded a baseline temperature of 24.8, a temperature ...
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1answer
61 views

Do I understand why heat capacity is called 'heat *capacity*'?

The notion of heat capacity seemed a little odd to me. I thought that the word 'capacity' could be throwing me off. Do I understand the notion correctly? I take the word 'capacity' to express, ...
2
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1answer
50 views

What is the enthalpy of formation of 1 mol of sulfuric acid?

In the contact process, the commercial process of producing $\ce{H2SO4}$, several reactions occur before the final product is produced: $\ce{S8_{(s)} +8O2_{(g)} -> 8SO2_{(g)}}~~~~~~~~~~\Delta ...
5
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2answers
59 views

Predicting melting points of substances based on their molecular/atomic structure

Wouldn't it be great to be able to predict the melting point of a metal based on the atomic number and not by looking in some table for the value that was measured experimentally by someone else? Or ...
2
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1answer
41 views

Why does raising the temperature affect the mass of dissolved solute? [closed]

Consider a solution of $\ce{KOH}$ which is in equilibrium with undissolved $\ce{KOH}$ at $25\ \mathrm{^\circ C}$. After raising the temperature to $50\ \mathrm{^\circ C}$, the mass of undissolved ...