lecture 5 thermo

Question 1

What is the second law of thermodynamics?

Answer 1

The second law of thermodynamics states that the total entropy of an isolated system can never decrease over time, and is constant if and only if all processes are reversible. Isolated systems spontaneously evolve towards thermodynamic equilibrium, the state with maximum entropy.

Question 2

Spontaneity is connected to what?

Answer 2

Change in enthalpy, Temperature and Entropy

Question 3

What are the two classes of exothermic reactions?

Answer 3

1. Reactions that are spontaneous at all T except O K

2. Reactions that can be spontaneous or non-spontaneous depending on T

Question 4

What are the two classes of endothermic reactions

Answer 4

1. Reactions that are non-spontaneous at all T

2. Reactions that can be spontaneous or non-spontaneous depending on T

Question 5

Disorder is a key factor in what?

Answer 5

Spontenaeity

Question 6

True or False? Things tend to become disordered and randomised

Answer 6

True

Question 7

What is Entropy (S)?

Answer 7

A measure of disorder

Question 8

What does disorder depend on?

Answer 8

How fast and far atoms/ions/molecules are moving around, how much rotation, vibration, bond stretching and, bending they are doing, and how many particles are in the system

Question 9

What is the unit for Entropy?

Answer 9

J K-1 mol-1

Question 10

The larger the S what?

Answer 10

The greater the disorder

Question 11

S is always what?

Answer 11

+ve

Question 12

What is the calculation for predicting entropy change in a reaction?

Answer 12

(Change in)S = S(final) - S(initial)

Question 13

Will increasing the temperature of a substance increase or decrease its Entropy? explain

Answer 13

It will increase the entropy as greater motion = more disorder

Question 14

True or False? There is a large decrease in Entropy when changing states

Answer 14

False, There is a large change in entropy when there is a change of state for example ice to water to steam causes large increases in entropy

Question 15

True or False? gas - liquid - solid = Greater entropy

Answer 15

True

Question 16

True or False? Smaller molecules have more entropy than larger molecules under the same conditions

Answer 16

False, Larger molecules have more entropy that smaller molecules

Question 17

Predict the entropy change for this reaction. 2H2(g) + O2(g) > 2H2O(g) ?

Answer 17

Decrease in entropy as the number of moles of O2 gas decreases

Question 18

Predict the entropy change for this reaction. NH4CL(g) > NH3(g) + HCl (g) ?

Answer 18

Increase in Entropy

Question 19

Predict the entropy change for this reaction. NaCl (s) > Na+(aq) + Cl-(aq) ?

Answer 19

Increase in entropy

Question 20

Predict the entropy change for this reaction. C(graphite) + O2(g) > CO2 (g) ?

Answer 20

Small increase as its going to fully gas

Question 21

Predict the entropy change for this reaction. H2(g) + Cl2(g) > 2HCl(g) ?

Answer 21

Cant say (moles technically stay the same)

Question 22

Predict the entropy change for this reaction. Water Freezes

Answer 22

Decrease in Entropy

Question 23

True or False? The amount of disorder is not always obvious

Answer 23

True

Question 24

What is the equation for delta rS?

Answer 24

Delta rS = products - reactants

Question 25

What is the 2nd law of thermodynamics?

Answer 25

The entropy of the universe increases in a spontaneous process and remains unchanged in an equilibrium process

Question 26

What is the equation for the 2nd law of thermodynamics?

Answer 26

Delta S universe > 0 for spontaneous reaction

Question 27

What is the equation for delta rS of the system?

Answer 27

(Products) - (Reactants)

Question 28

What is the equation for delta rS of the surroundings?

Answer 28

Because delta r H and T are involved in sponteneity they must be involved in delta rS for the surroundings therefore, Delta rS surroundings = -deltaH system / T

Question 29

What is Gibbs free energy?

Answer 29

A thermodynamic potential that can be used to calculate the maximum of reversible work that may be performed by a thermodynamic system at a constant temperature and pressure. DeltarH sys - T x deltarS sys

Question 30

When Delta G is <0, is the reaction spontaneous or non-spontaneous?

Answer 30

Spontaneous (-ve)

Question 31

When Delta G is >0, is the reaction spontaneous or non-spontaneous?

Answer 31

Non-Spontaneous (+ve)

Question 32

At equilibrium Delta r G = what?

Answer 32

0

Question 33

how do you convert between celsius and kelvin?

Answer 33

Kelvin = Celsius + 273.15.