A thermodynamic state function describing the total energy content of a system.

learn more… | top users | synonyms

-2
votes
0answers
20 views

How do you do this enthalpy change question? [on hold]

In the final stage of the production, the TiCl4 reacts with oxygen gas to form the TiO2, regenerating chlorine gas according to the equation: TiCl4(g) + O2(g) → TiO2(s) + 2Cl2(g) standard enthalpy ...
0
votes
0answers
6 views

Why is the enthalpy change of a hydrophobic compound more negative in a polar solvent than nonpolar?

I was under the impression that "like dissolves like" for both entropic and enthalpic reasons... According to my textbook: "From an enthalpy standpoint, even hydrocarbons are mores stable in aqueous ...
1
vote
2answers
119 views

Does ∆Gº exist?

To the best of my understanding, the quantity of Gibbs free energy of an entity depends on its concentration in the system. Equilibrium is reached when ∆G = 0, or when the Gibbs free energies of all ...
0
votes
1answer
39 views

For what is reaction enthalpy more relevant than reaction free energy?

I know enthalpy is a component of the Gibb's Free Energy (along with entropy). For practical purposes, though, isn't Gibb's Free Energy what a chemist is actually interested in, as that determines the ...
0
votes
0answers
13 views

Is it useful to calculate enthalpy of formation of complex compounds?

The typical textbook treatment of enthalpy of formation involves "elementary" compounds and bonds. How accurate would it be to use those tabulated values to calculate enthalpy of formation of complex ...
2
votes
3answers
68 views

Is ΔS of a system related to temperature and change in enthalpy?

I often see the equation $\Delta S_\text{universe}$ = $\Delta S_\text{surroundings}$ + $\Delta S_\text{system}$, where $\Delta S_\text{surroundings}$ can be re-expressed as $\dfrac{-\Delta H_\text{...
1
vote
0answers
19 views

Why is the specific heat of ethanol not representing experiments

I am in my last year of high school completing an assignment hot and cold packs, and particular the enthalpy behind them. My major lack of understanding is why my calculations are working for heat of ...
2
votes
2answers
50 views

Is the reaction of silver nitrate and copper endothermic or exothermic?

Is the following reaction endothermic or exothermic and why? $$\ce{2 AgNO3 + Cu -> Cu(NO3)2 + 2 Ag}$$ EDIT: I have a feeling that it is exothermic due to the fact that it is spontaneous and will ...
0
votes
0answers
21 views

What is the standard enthalpy change of solution of ethanol?

I was checking up on this data, and it greatly surprised me that no data tables or sources cite a value for this, as it is exceedingly common to mix ethanol and water. I suspect that it is quite ...
0
votes
0answers
23 views

Free energy of solvation of gases

I am calculating free energies of solvation and enthalpies of solvation from experimental Henry constants of solubility of CO$_2$ in cyclohexane. Free energy of solvation is obtained from the relation ...
0
votes
2answers
67 views

Understanding Gibbs free energy and enthalpy

Let's say that a reaction releases -50kJ/mol of Gibbs free energy (delta G), and -75kJ/mol of enthalpy (we know that -25kJ/mol went to make sure that the total entropy of universe increased). Now let'...
0
votes
0answers
14 views

How does the relative amount of oxidation of different alcohols affect the amount of energy released?

I am investigating the enthalpy of combustion of different primary alcohols and a website I found briefly mentioned how the relative amount of oxidation of different alcohols affects the amount of ...
0
votes
0answers
21 views

Trying to work out the Mean Bond Energy for C-H Bond

The question is asking me to find a value for the mean bond energy of the C-H bonds in Ethene and Ethane. I am given the mean bond energies for the C=C, the H-H and the C-C bonds which are 612kj/mol, ...
0
votes
0answers
11 views

Generalized enthalpy of vaporization for corresponding states

I'm interested in equations for substances at corresponding states that give general relationships between common chemical and physical properties. For example, the Guggenheim equation for saturation ...
0
votes
0answers
33 views

How can change in gibbs free energy be greater than enthalpy?

There is a problem in the textbook I'm studying Chemistry from that although was easy to compute, the result surprised me conceptually: The standard enthalpy for a reaction is said to be: -115kJ, we ...
0
votes
0answers
7 views

Exothermicity of reactions

Which of the following is the most exothermic: a) Sodium Bromide and Water b) Sodium Nitrate and Water c) Sodium Fluoride and Water d) Sodium Carbonate and Water e) Sodium Sulfate and Water I ...
3
votes
2answers
167 views

Why are there different values for enthalpy of combustion, depending on the calculation method?

For example: Combustion of Ethanol $\ce{C2H5OH(l) + 3O2(g) -> 2CO2(g) + 3H2O (l)}$ If i calculate this using enthalpy of formation: $\begin{array}{c|c} \textrm{Substance} & \Delta \ce{Hº (kJ/...
0
votes
0answers
35 views

What is the meaning of the double tilde in the enthalpy diagram?

My highschool book presents this diagram. I have searched the web and did not found the meaning of this ~~ tildes on y-axis.
0
votes
0answers
9 views

Predicting Extent of Exothermic Reactions

Sodium Acetate is widely used in hot packs due to the fact that it produces an exothermic reaction when it reacts with water. I decided to see if other sodium salts, such as sodium bromide, sodium ...
0
votes
1answer
76 views

Enthalpy change vs. change in internal energy in a system

I've been trying to get my head around the differences between enthalpy change and internal energy change for a system. Here's my understanding of it so far. I'd appreciate any feedback on my ...
1
vote
1answer
53 views

Standard Enthalpy of Formation of H2(g) vs H(g)

My question is somewhat related to this quesion. When I look at a table of standard values there are two entries for Hydrogen: $\ce {H2(g)} $ - 0 kJ/mol $\ce {H(g)} $ - 218 kJ/mol I understand ...
0
votes
2answers
33 views

Enthalpy change defined at constant pressure only?

Is change in enthalpy defined only at constant pressure? I know Q-W=del(U) And Q at constant pressure equals del(H) (enthalpy change). Can Q (heat given to the system) be used interchangeably ...
0
votes
0answers
21 views

Help with partial pressure question

For the reaction 3 O2(g) -> 2 O3(g), At 30 km above the surface of the earth, the temperature is about 230. K, and the partial pressure of oxygen is about 1.0 ✕ 10-3 atm. Estimate the partial ...
0
votes
0answers
18 views

Temperature when greater work leaving than heat entering

A reaction takes place in an open system where q is entering the system, work is leaving the system and the magnitude of q is less than w. The question (among others) is would the temperature of the ...
0
votes
2answers
24 views

Enthalpy and Internal Energy in Constant Volume Calorimeter

It is my understanding that enthalpy differs from internal energy only in that the change in enthalpy takes into account any pressure-volume work done on the system (or by the system) in a reaction, ...
0
votes
3answers
72 views

Intuition on Gibbs Free Energy

In many places, I read that Gibbs Free Energy is called "free energy" because some of the enthalpy that comes from the chemical reaction becomes "waste heat" due to a change in the entropy of the ...
0
votes
1answer
17 views

Finding the energy given out when 2 moles of reactants are mixed and ignited from a balanced equation

The question I am trying to answer is this: I only know about Hess' law, bond enthalpies and enthalpies of combustion and have tried to use all concepts in order to somehow get an answer but none of ...
0
votes
0answers
31 views

Entropy and enthalpy of hydrogen ion?

The absolute entropy of $\ce{H^+ (g)}$ is $\ce{108 kJ/mol.K}$. However, the absolute entropy of $\ce{H^+ (aq)}$ is exactly 0. Why is that? Also, the standard enthalpy of $\ce{H^+ (aq)}$ is 0, so ...
0
votes
2answers
78 views

derivation of enthalpy internal energy relationship [closed]

A question asks us to derive a relationship between the enthalpy change and the change in internal energy for a reaction. Now, I know the relationship is: $\Delta H = \Delta U + V \Delta p + p \Delta ...
0
votes
0answers
45 views

Difference between enthalpy and internal energy for a reaction

Zinc metal reacts with dilute nitric acid according to the equation: Zn + 2(HNO3) = H2 + Zn(NO3)2 calculate the difference between the delta H and delta U for this reaction at a temperature of 298 K....
0
votes
1answer
28 views

Finding value of equilibrium constant

I tried to find the value of equilibrium constant several times. I failed.. the value of equilibrium constant at 500K has enthalpy 250kJ/mol and entropy 48J/mol*K the answer is $ 2.45*10^{-24} $ ...
1
vote
0answers
34 views

Solubility Enthalpy of NaHCO3 [closed]

What is the solubility enthalpy of $\ce{NaHCO3}$ at 25 degree Celsius ($\mathrm{298K}$)?
3
votes
0answers
61 views

Theoretical temperature change in lime hydration

Calcium oxide (quicklime) and water have an exothermic reaction $\ce{CaO + H2O \rightarrow Ca(OH)_2} \quad \quad \Delta H^{\circ}_f=-65.3 \; \mathrm{kJ \cdot mol^{-1}}$ Assume that I have 1 kg of ...
6
votes
4answers
112 views

How much energy is stored when H+ is converted to H2?

I'm doing a write-up for this for my students: Source: Amirav Research Group (Facebook) The energy of formation of isopropyl alcohol is $-318.2~\mathrm{kJ/mol}$ (kilojoules per mole), that of ...
3
votes
2answers
185 views

Relationship between enthalpy change and endo/exothermic reactions

Something that confused me, is there a relationship between enthalpy change and endo/exothermic? Does region "x" represent the enthalpy change? What represents enthalpy change, kinectic energy, ...
8
votes
1answer
82 views

How is ΔH = q_v?

We know that: $$H = U + PV$$ $$\Delta H = \Delta U + \Delta(PV)$$ Now, If $P$ is constant, $$\rm \Delta H = \Delta U + P\Delta V$$ $$\rm \Delta H = q_p+w+P\Delta V$$ $$\rm \boxed{\Delta H = q_p}...
0
votes
0answers
12 views

How to use the enthalpy of formation to assess the energy stored in a molecule?

The standard enthalpy of formation for glucose is -2801 kJ/mol, while the standard enthalpy of formation for carbon dioxide is −393.5 kJ/mol. If one simply examine the numbers attached to the ...
8
votes
3answers
333 views

How to calculate an enthalpy change for this reaction

I've got an assignment to solve problem number 4 in this worksheet, that is to calculate change in enthalpy for reaction: $$\ce{CHCl3 + O -> COCl2 + HCl}$$ How do I solve it? Why is oxygen $\ce{O}$...
0
votes
1answer
57 views

Determining Enthalpy Change of the Combustion of Ethanol

A worked example went something like this: Use the following experimental data to determine the enthalpy change when 1 mole of ethanol (C2H5OH) is burnt: Mass of water = 150.00 g Initial ...
1
vote
1answer
171 views

Why are reactions of acids with metals exothermic?

I realised the other day that I'm not sure why the reactions of strong acids with metals are exothermic. Any reaction is exothermic if there's more energy released from bonds being made than is used ...
1
vote
2answers
109 views

(P1,T1) -> to (P2,T2) then what will be the change in enthalpy for ideal gas?

I need to prove that it is equal to the integral of $C_pdT$ from $T_1$ to $T_2$. But should not be the case only when the pressure is constant?
1
vote
0answers
15 views

Where can I find the standard enthalpy of formation for Sodium Cyanamide (Na2NCN)?

I am trying to find the standard enthalpy of formation for sodium cyanamide. Ive looked on various databases that list data about specific compounds but I can't find anything on this particular one. ...
0
votes
0answers
21 views

Find dE dissolution for salt

Part of my lab is to find the dEdissolution for a series of salts. I am told that dE ~ dH and a table which looks like this: Unfortunately in class we have never been given a lattice energy or ...
4
votes
1answer
42 views

When is the Assumption that Enthalpy is Constant over Temperature Change Invalid?

In a question, I was asked to integrate the Gibbs-Helmholtz equation to derive some formula. Then the next question asked: Identify one assumption that you have made in deriving the above equation ...
1
vote
0answers
58 views

How to calculate enthalpy change of neutralisation - what mass?

How to calculate enthalpy change of neutralisation - what mass? I made an experiment where I reacted 100ml HCL 2M with 100ml NaOH 2M in 1300ml Water, and got a temperature change dT. My question is ...
0
votes
0answers
46 views

Estimate bond strength from bond energies

The standard enthalpy of formation for NO(g) is 90. kJ/mol. Use this and the values for the O=O and N≡N bond energies to estimate the bond strength in NO. Attempted work: 90= 2(NO) - (941+495) NO = ...
3
votes
0answers
29 views

Enthalpy change with temperature

Recently I stumbled across a book that describes enthalpy change with temperature, specifically for a product of combustion process (e.g. CO as a result of solid carbon combustion). The book says that ...
1
vote
0answers
26 views

Energy required to break salt bridges in peptides and proteins

Is there a way to calculate the energy required to break a salt bridge in a peptide or on the exposed surface of a protein in aqueous solution? Is there any useful literature on this topic? I'm ...
0
votes
0answers
22 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 ...
3
votes
2answers
109 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 $...