Thermochemistry

Question 1

What is Thermochemistry?

Answer 1

The branch of chemistry which studies energy changes that accompany physical, chemical, or nuclear changes. Also a term used to describe the study of energy and energy transfer.

Question 2

First Law of Thermodynamics

Answer 2

The energy of the universe is constant: E(universe)=0

Question 3

Surroundings

Answer 3

The matter surrounding the system which is capable of absorbing or releasing thermal energy.

Question 4

Exothermic

Answer 4

Sys transfers heat to surroundings and thus the temp of the surrounding inc. (comb, freezing, condensation)

Question 5

Endothermic

Answer 5

Sys absorbs heat from surroundings thus temp of surroundings decreases (melting, vaporization)

Question 6

Open system

Answer 6

matter and energy can escape

Question 7

Closed system

Answer 7

matter can’t escape but energy can

Question 8

Isolated system

Answer 8

matter and energy can’t escape (ideal)

Question 9

Calorimetry

Answer 9

process of measuring energy changes in a chem sys. nΔH(x,sys) = -mcΔT(sur)

Question 10

Calorimetry (Heat measurement)

Answer 10

q=mcΔT

Question 11

Molar Enthalpy

Answer 11

Enthalpy change associated when 1mol of a substance undergoes a physical/chem/nuclear change. (J/mol)
ΔH(sys) = nΔH(x)

Question 12

Thermochemical Equation

Answer 12

A balanced chem equation that indicates the amount of heat that is absorbed or released.

Question 13

What are the 4 different methods for communicating thermochem equations?

Answer 13

Energy term, Enthalpy value, Molar enthalpy, Diagrams

Question 14

How to write a thermochem equation with energy term?

Answer 14

(In equ.) Energy as reactant is endo, energy as product is exo. Ex. H20(g) + 285.8 kJ -> H(2,g) + 1/2 O(2,g)

Question 15

How to write a thermochem equation with enthalpy value?

Answer 15

Next to equation. + is endo, - is exo.

Question 16

Bond Energy

Answer 16

Energy to break is endo, energy released is exo.

ΔH = ΣR BondEnergy - ΣP BondEnergy

Question 17

Communicate thermochem equation with Diagram?

Answer 17

Exo goes down (down arrow), endo goes up (up arrow)

Question 18

Hess’s Law

Answer 18

ΔH = ΣΔH of individual steps.
Ex. ΔH = …
ΔH = …

Question 19

Enthalpy of Formation

Answer 19

ΔH = ΣnΔH(f,p) - ΣnΔH(f,r)

Question 20

3rd Law of Thermodynamics

Answer 20

Entropy(S) = 0 at T=0 K

Question 21

Law of Entropy

Answer 21

+entropy considered spontaneous
Order-disorder ΔS>0 (+)
Disorder-order ΔS<0 (-)

Question 22

Increasing (S) Physical Change

Answer 22

Volume inc, temp inc, state change, dissolving

Question 23

Increasing (S) Chem Change

Answer 23

more n on prod side than react, complex molecule broken to many smaller comp, solid reactant but prod are gas/liquid

Question 24

Entropy

Answer 24

ΔS = ΣnS(p) - ΣnS(r)

Question 25

Gibb’s Free Energy (G)

Answer 25

ΔG = ΔH - TΔS

Question 26

Meaning of ΔG

Answer 26

ΔG<0 rxn is spont. in forward direction (release energy)
ΔG>0 rxn is non-spont. in forward direction (req energy)
ΔG=0 rxn is @equilibrium (spont. in both directions)

Question 27

What makes spontaneous?

Answer 27

Endo (ΔH>0): +entropy - spont depends on T
-entropy - non-spont
Exo (ΔH<0): +entropy - spont @ all T
-entropy - spont depends on T