For questions relating to energy required for or produced by reactions, including questions of endothermicity/exothermicity, bond enthalpy, etc.

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Why are hydrogenation reactions exothermic?

I learnt that all reactions that yield hydrogen are endothermic (such has reforming) and reactions, that use up hydrogen, are exothermic (FCC cracking, hydrogenation, etc.). But why is this so? I know ...
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2answers
195 views

Why is activation energy temperature independent?

I know that activation energy for a reaction is the extra energy given to the reactants to reach the threshold energy so that they can collide and react. But then, why is it said that the activation ...
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27 views

Using electron affinity to calculate lattice energy

I am trying to calculate the lattice energy of $\ce{CaBr2}$, I am uncertain of how to incorporate the electron affinity value provided for $\ce{Br2}$ into my calculation. Since electron affinity is ...
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12 views

Chemical energy + energy of electrons

The amount of energy released in a chemical reaction is equal to variation of the enthalpy of this system (In general). The energy released is usually is in form of light and heat. When light is ...
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2answers
71 views

What is the qualitative definition of enthalpy in beginner terms?

So in my coursebook it says enthalpy is a property that accounts for the increase in internal energy and the accompanying work done by the system and that its equal to the sum of the internal energy ...
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1answer
24 views

Positive vs. negative heat of solution confusion

Given that I have absolutely zero formal (or informal) education in chemistry (sorry about that), I'm struggling to get my head around what appears to be repeated confusions of the term "heat of ...
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1answer
57 views

How does ice melt?

I know that when water freezes, it forms a crystalline structure created by the hydrogen bonds between polar water molecules. Also, I know that during a phase change, the potential energy of the ...
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31 views

Calculating energy change for calcium carbonate decomposition

The $\Delta H^0$ for the decomposition of $\ce{CaCO3(s)}$ is $178.3~\mathrm{kJ/mol}$ at $25~\mathrm{^\circ C}$ and $1.000~\mathrm{atm}$. What is the $\Delta E$ for the decomposition process? ...
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34 views

What factors effect the energy change in a reaction?

The reaction of zinc metal and copper sulfate solution produces copper metal and zinc sulfate solution. What factors affect how much energy is given out for this reaction? So far I have:The mass of ...
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34 views

Calculate the heat of a reaction

Say I would like to calculate the heat produced by the following reaction: $$\ce{2SO2 + O2\longrightarrow2SO3}$$ I have calculated the moles of the reagents. I can't seem to figure out how to ...
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27 views

How to prove that the forward and reverse reactions have the same rate at equilibrium?

I was trying to answer a question from Zumdahl and Zumdahl's Chemistry textbook which asks me to show that the rate constant K is related to the forward and reverse reaction constants: ...
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38 views

When is a reaction feasible at room temperature?

Gibbs free energy determines whether a reaction will occur spontaneously or not. Still, the activation barrier of a reaction determines if a reaction will occur at a given temperature. At any non-zero ...
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2answers
86 views

Interaction between energy and entropy in highly elastic polymers?

Consider the interaction of energy and entropy in the highly elastic materials of an ideal polymeric network. Now Gibb's free energy cannot be used directly $\Delta H = \Delta G + T \Delta S$ where ...
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52 views

Calculating the energy released in cooling an ideal gas

Calculate the amount of energy released in cooling an ideal gas using the following information. Temperature change: 25 degrees celsius to 0 degrees celsius Volume of container: 5 litres (remains ...
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2answers
336 views

Does the potential energy increase when temperature is raised?

The potential energy of a material is its ability to do work. So I would suspect the potential energy to increase during phase changes that increase entropy (solid $\rightarrow$ liquid and liquid ...
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1answer
52 views

Formation enthalpy vs. bond enthalpy

I have been working with thermochemistry at school for a while. I have been introduced to the two terms: formation enthalpy and bond enthalpy. However, I have not quite understood the difference ...
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1answer
55 views

Change in Gibbs free energy of vaporization reaction

In my chemistry book, I see the equation $$\Delta G_{rxn} = \Delta G_{rxn}^0 + RT \ln(Q)$$ where $\Delta G_{rxn}^0$ is the change in Gibbs free energy under standard conditions (1 atm pressure in ...
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2answers
135 views

Does Gibbs free energy of formation always equal zero for elements in standard state?

I was looking through the appendix in my chemistry textbook when I noticed that every compound that had a $\Delta H_f$ of zero also had a $\Delta G_f$ of zero. So of course the compounds that have a ...
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2answers
196 views

Freezing/Melting of water and gibbs free energy

I get that $\Delta G$ measures the spontaneity/capacity of a system to do non-mechanical work, and that if: $\Delta G > 0$, the reaction is not spontaneous $\Delta G < 0$, the reaction is ...
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29 views

Calculating the wavelength of an emitted photon of a Ne^9+ ion

I'm supposed to calculate the wavelength of an emitted photon going from the 6p orbital to the 2s orbital. The first part of this problem will be to use the equation $$E=-{Rh\over n^2}$$ in order ...
3
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2answers
81 views

Most energy-dense commercial battery available

What's the most energy-dense and currently commercially available chemical battery technology? Would it be the Lithium-Ion Polymer or has it been surpassed already? There's is a chemical ...
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2answers
698 views

Is iron the most stable element in the periodic table?

According to the binding energy per nucleon vs mass number graph, it is observed that iron-56 has the maximum value of binding energy per nucleon (8.75 MeV).It means that Iron-56 is the most ...
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16 views

Origin of different colour for thio analogue of indigo from blue to red

Why the thio analogue of indigo is red? What is the reason behind change of colour from indigo to red just by change of N to S. What I get is that there will be electronegativity, lone pair ...
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1answer
88 views

What is the exact definition of state functions? How to determine state functions?

How do you know if something is a state function? I know Internal Energy (U) is a state function since it is the sum of energies, which is constant at a given time. However I don't know for sure if ...
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2answers
47 views

Understanding the bond dissociation energy of poly-atomic molecules

Now I have a breaker which is containing $\ce{CH4}$ of some amount at standard conditions and then I put it on a burner. In Thermodynamics we are taught about how to find the bond enthalpy of ...
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1answer
37 views

Is it possible to recycle an alkaline battery?

Is it possible to recycle an alkaline battery? The application I am thinking about is that in 3rd world countries often access to western markets is limited. You can't just pop into a store and buy ...
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106 views

How to find out the energy gained from hydrolysis of Dimethylsulfoniopropionate?

I am trying to find out what the energy gain from hydrolysis of DMSP (Dimethylsulfoniopropionate) is, versus the energy gain from oxidation of a sugar or carb (e.g. glucose) in a terrestrial ...
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71 views

Torsional energy diagram for toluene

Exercise: Sketch a complete (360 degree) torsional itinerary for toluene. My take: Well it's only for 300 degrees - the pattern continues by one hill more. Energy (strain) is plotted on the ...
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11 views

Voltaic Cells and Redox

If I had a magnesium electrode dipped in a magnesium sulfate solution and an iron electrode dipped into iron (III) sulfate solution... Am I right in thinking that you need to identify the oxidation ...
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1answer
22 views

Spectroscopy and Excitation of Electrons

As metals are heated, they glow white and then blue. How might you explain this change in color as the temperature of the metal is increased? My answer consist of the idea that with increased thermal ...
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2answers
73 views

How does the Lennard-Jones potential relate to energy?

Considering the Lennard-Jones potential, $$V(r)=\frac{A}{r^{12}} − \frac{B}{r^{6}}$$ How does this relate to force or energy? I suspect that there is some physics equation I'm forgetting. I know ...
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0answers
21 views

Understanding the energy produced from oxidizing 1 kg of lithium

I am reading the following paper in preperation for a research project on the theoretical energy density of batteries: Lithium - Air Battery: Promise and Challenges and on the second page they ...
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1answer
113 views

How to calculate the boiling point of a solid substance?

Say that I have a solid substance; I know its density, mass, volume, melting point, specific heat, the pressure which it is under, and nothing else. (for now.) How do I find the heat at which it ...
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24 views

Why is helium a liquid at absolute zero? [duplicate]

Why is helium a liquid at absolute zero? And why is it the only non-solid element at 0K? At 1 atm.
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1answer
36 views

Energy a system at room temperature can supply?

"This reaction requires XYZ activation energy, therefore it cannot happen at room temperature." is a sentence I find often in organic chemistry textbooks. Activation energies are steadily given in ...
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1answer
152 views

What are the effects of the repulsive forces between electron on the potential energy graph for the dihydrogen molecule?

This diagram is from my textbook. It states that as long atoms get closer, the energy decreases due to the attractive forces between the electrons and the nuclei. When the nuclei get too close, the ...
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1answer
33 views

Why grain boundary is reactive to acid?

I have read about grain boundary etching. They use acid to make grain boundary visible for light microscope. I know that grain boundary is reactive to acid, but why? Thanks.
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69 views

Molar heat of reaction for water in a neutralization reaction

I have a simple lab problem: $30\ \mathrm{mL}$ of $1\ \mathrm{mol/L}$ $\ce{H2SO4}$ reacts with $50\ \mathrm{mL}$ of $1\ \mathrm{mol/L}$ $\ce{NaOH}$ in a neutralization reaction as per the following ...
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1answer
103 views

Difference between dissociation energy and dissociation temperature for water?

I was trying to find the temperature at which water dissociates into hydrogen and oxygen, and so I came across this Wikipedia page. It states that it takes 493.4 kJ/mol + 424.4 kJ/mol to dissociate ...
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108 views

Bond Energy Calculation

Dichlorine monoxide (which has the skeleton $\ce{Cl‐O‐Cl}$) is an unstable molecule and explodes readily to form chlorine gas and oxygen gas. The heat of the reaction $\Delta ...
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37 views

How to find the energy difference between two newman projections?

I understand that question 16 is d. However, for question 17 I cannot understand how to use those numbers to determine. I asked this question on another site and they said d. 3.6, however they did ...
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358 views

Is the Gibbs standard free energy always constant?

I am a biochemistry student and we are learning about thermodynamics. Is the Gibbs standard free energy for a reaction always constant? The equation below suggests that it changes with temperature: ...
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50 views

Could the net equations for burning hexene be used as a means of energy source?

$6\ce{CO_2} + 6\ce{H_2O}\xrightarrow{some\;catalyst}9\ce O_2 + \ce{C_6H_{12}}$ $\ce{C_6H_{12}} + 6\ce O_2\to 6\ce{CO_2} + 6\ce H_2$ $6\ce H_2 + 3\ce O_2\to 6\ce{H_2O}$ At one point, I had made a ...
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2answers
104 views

Conceptual doubt about Gibbs free energy

At constant pressure, which is the usual condition for chemical reactions, heat absorbed/released by the system is the same thing as enthalpy change. According to the Gibbs equation, $$\mathrm dG = ...
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1answer
137 views

Calculation of non-bonded interaction energies (Organic Molecule)

If one were to calculate the non-bonded interaction energy between two atoms this would equate to the sum of vdw + electrostatic potential energy. Could anyone please explain how I could calculate ...
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1answer
25 views

Energy in molecules

A textbook states: Fats also provide an efficient way to store energy over long time periods, since they contain over twice as much energy per gram as carbohydrates What's the chemistry ...
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1answer
105 views

Calculation of the lowest energy conformation with a webbased solution or freeware

I like to draw a molecule in different conformations in a) website or b) freeware and Calculate its relative energy difference (for example to the lowest global energy conformation) Display the ...
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1answer
64 views

The conversion of energy during electroplating

I've made a test and i've faced a problem with a part of a question which says: "What is the conversion of energy occuring in electroplating? " I answered that it is conversion from electric energy to ...
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1answer
69 views

Uniform circular motion of electrons?

Can we use the uniform circular motion formulae to calculate the velocity of an electron along with the formula of radius of nth Bohr orbit? And using that can we calculate the kinetic energy of an ...
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2answers
312 views

Physical Interpretation of Gibbs Free Energy

I know that $\Delta G = \Delta H - T\Delta S$ and that if $\Delta G$ less than $0$ a reaction will be spontaneous. What I am wondering is what is the actually physical interpretation of Gibbs free ...