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

learn more… | top users | synonyms

0
votes
1answer
15 views

percent ionization explanation [duplicate]

Using a weak acid as an example: $$\ce{HOAc <=> AcO- + H+}$$ The position of this equilibrium shifts to the right with increasing dilution. I have found textbooks that say this, but do not ...
7
votes
1answer
51 views

Ag-Sn-Cu Phase diagram to formulate homogenization temperature / duration

I am working on Ag-Sn-Cu alloy phase diagram to figure out the best temperature / duration to homogenize the alloy (annealing). The %age of elements in the alloy are Ag - 40 % Cu - 27.8% Sn - 32.2 % ...
5
votes
0answers
25 views

Seeking titanium compound, melting point <1600 °C, decomposes to TiO

The title says it all. I’m new to glass making, and I need a titanium compound that will render me $\ce{TiO}$ through decomposition, and has a melting point under 1600 °C. Hopefully I can get one ...
2
votes
1answer
58 views

Why does attraction always cause release of energy making the system more stable?

Suppose $\ce{Na^+}$ and $\ce{Cl^-}$ form an ionic bond. In doing so they will come closer by attraction. Now as they come closer their speed will increase and hence the kinetic energy increases. So ...
0
votes
0answers
19 views

Freezing point of multiple solute solution

I have 4 solutes, iron, sulfate, sulfuric acid, and peroxide. This is diluted in water and I have the molalities in mol/kg ($0.5, 0.1, 0.4, 0.35$). I tried using $\Delta T_f=−K_f\times m$, where m is ...
2
votes
1answer
48 views

Calculating enthalpy per gram mole of oxygen bond in haemoglobin

A solution of $5\ \mathrm{g}$ of haemoglobin in $100\ \mathrm{cm^3}$ of solution shows a temperature raise of $0.031\ \mathrm{^\circ C}$ for complete oxygenation. Each mole of haemoglobin binds $4\ ...
1
vote
2answers
35 views

What happens when heating water in a pressure vessel?

Suppose that I take a pressure vessel that can withstand up to 2000 PSI. Now I fill it with water (not completely, but around 90%) and start to heat it with a direct flame. What I want to know is, ...
4
votes
2answers
42 views

How is change in entropy of universe related to the energy released by system that can be used to do work?

What does change in entropy ($\Delta S$) represent ? How does change in entropy of a universe ($\Delta S_{univ}$) give us information about energy available to do work. I would like to know the ...
2
votes
0answers
23 views

Is there no irreversible way of moving between two equilibrium states at constant T and P?

There's a reaction occurring at constant $T$ and $P$, and it is in chemical equilibrium. Now by adding infinitesimal quantities of reactants, it is taken to another equilibrium state in a reversible ...
1
vote
0answers
20 views

Thermodynamic-Fuel and efficiency

Why is the maximum theoretical efficiency of Ar engine higher than that of Nitrogen engine? On a molecular level. For an Otto Cycle $\mathrm{Eff} \le\left(1-r^{1-\gamma}\right)$ ...
0
votes
1answer
18 views

Molar enthalpy vs Enthalpy of formation?

(Note I've refocused a previous unanswered question into a more general question. You can find the original much more specific question here) There seems to be two main ways of looking at the enthalpy ...
3
votes
3answers
102 views

Trying to Understand Entropy

I'm currently looking at Principles of Chemistry by Atkins, and I have a few questions involving entropy. These questions probably arise from my poor understanding of reversible/irreversible ...
3
votes
1answer
47 views

Heat capacity of mixtures

After reading this recent question I was interested in how to calculate the specific heat capacity of a mixture based on the specific heat capacities of its components. According to this website the ...
0
votes
0answers
19 views

Using equilibrium constant in gibbs equation [duplicate]

In my chemistry textbook, it is written that : Gibbs energy for a reaction in which all reactants and products are in standard state, $\Delta_\mathrm{r}G^\circ$ is related to the equilibrium ...
6
votes
1answer
105 views

What is the proper term for lines of constant volume and constant enthalpy on a thermodynamic diagram?

I know an isotherm is a line of constant temperature. Isobar is a constant pressure line. Isentrope is a line of constant entropy. But what do you call a line of constant volume? An Isochore? And ...
3
votes
1answer
37 views

Maximum Useful Work from a Process

Negative of the $\Delta G$ for a process is the maximum useful work that can be obtained from it (at constant pressure and temperature). I understood this in this way: $\Delta H$ is the heat absorbed ...
-1
votes
1answer
39 views

How to Get Ideal Gas Constant R for Two Gases Mixed

One cubic container contains a mixture of gases composed of 0.02 kgmol of oxygen and 0.04 kgmol of helium at a pressure of 220 kPa. What is the temperature of this ideal gas mixture in Kelvin. ...
3
votes
1answer
31 views

Is it possible to calculate specific heat capacity of a compound based on its elements' heat capacities?

What the question says. For example, if I knew the specific heat capacities of lithium and oxygen, could I work out the specific heat capacity of lithium oxide with no further information?
1
vote
0answers
27 views

calculate diffusion coefficient from MSD vs time [closed]

I have a trajectory file from simulation of 20,000 frames with 5 ps time in between every frame, what I want to do is to calculate diffusion in 2 dimension (x and y axis). but to calculate diffusion ...
1
vote
1answer
20 views

Is enthalpy of a reaction meaningful at variable pressure?

Why should the enthalpy of a reaction be defined at constant pressure. Why can't it be defined at variable pressure?
0
votes
1answer
39 views

Isentropic Process Nitrogen with Pressure Ratio

Nitrogen (k=1.4) is expanded isentropically. Its temperature changes from 620°F to 60°F. Find the Pressure Ratio: Answer is 12.91 Simply use Isentropic Relation. $$620°F = (1799/3) K$$ $$60°F ...
3
votes
0answers
55 views

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
votes
0answers
41 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 ...
0
votes
1answer
26 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 ...
-1
votes
0answers
11 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 ...
0
votes
0answers
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
votes
1answer
62 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 $\ce{B}$ ...
-1
votes
1answer
48 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
votes
1answer
90 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
votes
1answer
65 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
votes
1answer
42 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
votes
0answers
82 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
votes
1answer
32 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}} + ...
1
vote
1answer
63 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
94 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
votes
1answer
81 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
votes
1answer
48 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
votes
1answer
24 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
220 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
37 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
votes
2answers
122 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
votes
2answers
463 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 ...
1
vote
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 ...
-1
votes
1answer
62 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?
0
votes
0answers
42 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 ...
2
votes
1answer
57 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. ...
0
votes
1answer
52 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\ ...
3
votes
0answers
28 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
votes
2answers
48 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. ...