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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3
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1answer
665 views

Electrode potentials at interfaces?

My questions relates to the fundamental concept of electrochemistry, more specifically the electrode potentials. 1) First, why is there a potential difference at the interface of two phases? ...
45
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4answers
3k views

Unit of the equilibrium constant: contradiction of Bridgman's theorem?

The following equation is standard in thermodynamics: $$ \Delta G^\circ=-RT\log(K) $$ where $K$ is the equilibrium constant. In dimensional analysis, Bridgman's theorem tells us that the argument ...
3
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1answer
366 views

Would concentration of a compound in equilibrium increase even if it's not favored by a volume decrease?

So say I have a reaction where there are x moles of gas on the reactant side, and y moles of gas on the product side, where x>y. The volume decreases, favoring the products side. The textbook I am ...
2
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1answer
3k views

Why doesn't diffusion take place between immiscible liquids?

If we take a test-tube of bromine and invert an upside-down test tube of air on top of it, it'll diffuse with the air, until the bromine is thoroughly 'mixed' with the air in both test tubes. But why ...
6
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2answers
11k views

Azeotropes and separation by distillation?

I have just recently learnt the theory of fractional and normal distillations and the basics of maximum and minimum boiling azeotropes. Most books say that the components of the mixture forming an ...
3
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1answer
2k views

Why are partial molar Gibbs energy and Gibbs energy per mol equal?

I'm not a chemist, but I need some insight into chemical thermodynamics. In the book that I'm reading (Nevers, 2012), equation (4.28) relates the chemical potential of a pure species to it's Gibbs ...
2
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1answer
99 views

Would cooling of a battery using cooler affect its life time?

My smartphone gets over heated where I use mobile data for long period. Last day I found a cooler of an old cpu, the thing silver in colour to absorb heat(with eventually gives out heat as it has more ...
24
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1answer
243 views

When measuring avidity should you use the ligand concentration or the nanoparticle concentration?

Looking at avidity between a ligand-receptor, you're looking at an enhancement of the $K_d$ compared to a lone ligand. Is it more appropriate to compare the $K_d$ using the concentration of the "...
28
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4answers
95k views

Difference between exothermic and exergonic

In High School I learned that an exothermic reactions releases energy, while an endothermic reaction needs energy to occur. Now I learned that there is a separate, somewhat similar classification ...
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1answer
2k views

Lower Heating value calculation from chemcial combustion equation of Butane

QUESTION Butene, C4H8 is burned in an engine with a fuel-rich air-fuel ratio. Dry analysis of the exhaust gives the following volume percents: $\ce{CO2} = 14.95%$, $\ce{O2} = 0%$...
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4answers
303 views

Can you color a flame and what would the effects be?

I read this question (Flame temperature for cooking food) and came up with the following questions: Could companies color their flames so that products would heat quicker? How would they do this? ...
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0answers
1k views

Entropy and racemization?

The process of racemization of an optically compound is entropy driven and hence nature prefers a racemic mixture to an optically active one, which is consistent with the idea of the intuitive ...
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2answers
1k views

Chemical Equilibrium - Why does changing the temperature shift the equilibrium?

I know that raising the temperature in a reversible chemical reaction causes the equilibrium to shift to the endothermic side. I know that $\Delta G = \Delta H − T\Delta S $ but I don't know how to ...
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0answers
34 views

Chemical Equilibrium - Why does changing the temperature shift the equilibrium? [duplicate]

I know that raising the temperature in a reversible chemical reaction causes the equilibrium to shift to the endothermic side. I know that $\Delta G = \Delta H - T \Delta S$ but I don't know how to ...
7
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4answers
20k views

Why won't water freeze if you put ice in it, despite ice being frozen?

Just now I got some room temperature water and added some ice to cool it, and it just came to me, like the scientist I wish I was ... why doesn't frozen (freezing point) ice added to higher ...
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1answer
6k views

Liquid with low specific heat and high thermal conductivity (relative to water)?

As the title suggests – does there exist a liquid with a lower specific heat then water but with a higher thermal conductivity? I thought of this in the context of sous vide cooking: Ideally, the ...
9
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4answers
81k views

Why calcium chloride is used to melt ice over sodium chloride

I'm not quite sure I understand this. My question is: Calcium chloride is a salt used widely to melt ice on sidewalks and roads. Explain why one mole of $\ce{CaCl2}$ would be more effective than ...
6
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2answers
38k views

What does it mean for a reaction to favor the reactants/products?

(This example is purely hypothetical.) You have the reaction $$\ce{H2(g) + O2(g) <=> H2O2(g)}$$ at $T = 500\ \mathrm{K}$. The reaction reaches equilibrium at the following concentrations: $$\...
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1answer
3k views

How do I know if concentration of Ammonia affected my absorbency measurements?

This is for determination of copper in a penny Lab. After making standard solutions we made a solution with a penny, dissolving it in nitric acid and adding ammonium hydroxide to form a more ...
4
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1answer
217 views

Entropy, enthalpy, and reversibility

In my introductory chemistry course, we learned that for reversible processes, entropy is defined as $ΔS = q/T$. However, we did not spend that long on this before moving on to other things like Gibbs ...
3
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1answer
295 views

Michaelis Menten derivation for 2 enzyme substrates

We know the Michaelis Menten derivation for the following reaction: $$\ce{E + S <=> ES -> E + P}$$ However, what if the reaction took place in a different scenario whereby: $$\ce{E + S <...
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1answer
4k views

How hot can Thermal Grease get?

Thermal Grease is used to remove the air gaps between CPU and heatsink. However, computing aside, what would determine the max temp that the grease can handle before it burns or breaks down?
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1answer
264 views

Thermodynamic Cycle

What is the value for $\Delta_f G^0(\ce{Cl^-}, \ce{aq})$ in this thermodynamic cylce: Do you agree it should be (with the formation free energy of $\ce{H^+} = 0$) $$-\Delta_f G^0(\ce{Cl^-}, \ce{aq}) ...
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1answer
2k views

How is hydration free energy of a solute measured experimentally?

I am reading a paper (Shirts, M. R.; and Pitera, J. W. and Swope, W. C. and Pande, V. S. J. Chem. Phys. 2003, 119, 5740-5761). Near the beginning of the paper (page 5745), the authors state: ...
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2answers
12k views

When is it okay to use $Q=mc\Delta T$, is this equation only for calorimetry questions?

When is it okay to use $Q=mc\Delta T$, is the equation only for calorimetry questions? When a question talks about heat how do I know if i'm measuring $\Delta H$ or Q?
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1answer
200 views

Spontaneous inequilibrium in a gas in an isolated system?

Can an isolated system(of several phases) in equilibrium by itself move out of equilibrium? if a system contains for example an inflammable gas dispersed with another combustible gas such that the ...
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2answers
525 views

Measuring Thermodynamic Stability

We can predict whether a reaction can occur spontaneously by calculating the change in Gibbs' free energy. I was just wondering whether there is any general measure of the thermodynamic stability of ...
2
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2answers
1k views

Hot and cold air interaction in a sealed environment

What would happen if air heated to 1200 degree's Fahrenheit in a sealed environment was injected with colder air? No specific pressure defined yet just a general idea of potential interaction between ...
3
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1answer
521 views

Influence of solubility on the complexation constants at different pH values

Given some small chemical compounds whose solubility varies with pH, and in the case of compounds that can form complexes, I have seen that the complexation constant varies with pH. I think there ...
3
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1answer
100 views

Nitrogen triodide energetics

Ammonia has a heat of formation of $-46 \:\mathrm{kJ/mol}$ (which means that it's formation from the elements releases heat). When mixed with iodine at room temperature, it makes nitrogen triodide (...
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1answer
121 views

Is it possible to form bubbles of ionized hydrogen and ionized oxygen under the right pressure/temperature conditions during electrolysis of water?

When we run a current through water (pure or not), $\ce{O_2}$ forms at the anode while $\ce{H_2}$ forms at the cathode. If I understand correctly, as water is already slightly ionized, $\ce{H}$'s snap ...
2
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1answer
347 views

Software for chemical reaction simulation in ICE

I want to study what happens in a internal combustion engine in which fossil fuels are mixed along with other chemical additives. Example: Acetone drastically reduces surface tension. Most fuel ...
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2answers
755 views

Calculating heat capacity of a calorimeter

I am struggling on this question : The heat of neutralization of $\ce{NaOH}$ and $\ce{HCl}$ is $-57.1\:\mathrm{kJ}$, calculate the numbers of moles of $\ce{HCl}$ and if $x$ moles of $\ce{HCl}$ were ...
37
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5answers
109k views

Difference between thermodynamic and kinetic stability

What is the difference between thermodynamic and kinetic stability? I'd like a basic explanation, but not too simple. For example, methane does not burn until lit -- why?
14
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5answers
28k views

What is a pure substance?

I found as I was preparing to teach "Introduction to thermodynamics" that there are varying definitions or examples of pure substances. For instance the text book I have to use "Thermodynamics an ...
4
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1answer
4k views

What defines matter's phase at room temperature?

So, a simple question: what makes neon a gas; what makes water liquid; what makes plutonium-238 a solid at room temperature? Of course, the phase is determined by the excitation of the molecules, but ...
5
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1answer
229 views

Lennard Jones liquid vapor phase transition

I am trying to generate a phase diagram of pressure versus temperature in a NPT ensemble using molecular dynamics method. I am using the Lennard Jones potential with 108 particles and Berendsen ...
5
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1answer
274 views

Source for thermodynamic and/or transport properties

I'm working on some combustion problems using Cantera and I can't find references for the thermodynamic or transport properties for many of my chemical species. I'm looking for NASA-7 or NASA-9 curve-...
3
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2answers
567 views

Non-Commercial Thermal Insulation

I am trying to create a small 10 to 20cm cube that can conserve the heat in 100 to 200ml of 60-90c water in a small Pyrex glass for about an hour. The problem is that I can not use commercial ...
3
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1answer
1k views

Why can dissolution reactions (e.g. dissolution of calcium chloride) be exothermic?

Dissolution reactions are normally endothermic, and crystallization reactions are normally exothermic, but there are some exceptions -- such as the dissolution of calcium chloride. Why is this so?
11
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4answers
15k views

Maximum temperature attainable by thermite reaction

In the thermite reaction $$\ce{2Al(s) + Fe2O3(s) -> 2Fe(l) + Al2O3(s)}$$ what is the maximum temperature attainable by the products? Assume reactants at $25\ \mathrm{^\circ C}$ and $1\ \mathrm{...
7
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1answer
6k views

Is an explosion merely an exothermic reaction?

An exothermic reaction is apparently one that releases energy to it's environment. According to Wikipedia, an explosion is a rapid increase in volume & energy. Does this mean that an explosion is ...
1
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1answer
830 views

Determining enthalpy and internal energy of formation for potassium superoxide

Given $2.14\ \mathrm g$ of $\ce{K(s)}$, determine $\Delta H^\circ_\mathrm{f,m}$ and $\Delta U^\circ_\mathrm{f,m}$ for $\ce{K2O}$. We know: The calorimeter's constant: $1849\ \mathrm{J\...
5
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1answer
501 views

Find mass of CO₂ and heat released per minute in a combustion reaction

I am not sure where to start with this problem. I know that $\small q = mc(T_f-T_i)$, but that seems like it would not help here. I think I need to balance the equation, but I am not sure how the rate ...
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3answers
6k views

Looking for a safe exothermic reaction [closed]

Is there an exothermic reaction which produces 1 to 2 minutes of heat at around 175 degrees Fahrenheit, no toxic gasses and is considered to be more or less safe?
1
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1answer
2k views

Should I use specific heat to calculate how much fuel is required?

Question: A backpacker wants to carry enough fuel to heat $\pu{3.0 kg}$ of water from $\pu{20 ^\circ C}$ to $\pu{100.0 ^\circ C}$. If the fuel he carries produces $\pu{36 kJ}$ of heat per gram when ...
7
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1answer
874 views

Why is bread warm at room temperature?

If I buy a loaf of freshly-made bread and leave it out at room temperature for a day or two, when I reach into the bag the air inside is much warmer than the rest of the room. Why?
2
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1answer
93k views

How do you calculate molar specific heat?

I know how to calculate the specific heat, but not molar specific heat. What is molar specific heat and how do you calculate it?
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2answers
3k views

Calculating entropy: why consider a reversible path?

I am reading up on entropy in a textbook and I got confused by this: It says that to calculate the entropy for an irreversible process using heat flow, one must imagine the reversible process in ...
20
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3answers
5k views

What are the chemical reactions behind fire?

I've always wondered what the chemistry behind fire is. What are the basic chemical reactions behind a simple wood fire, and how do they manifest into this phenomenon?