Reaction Feasibility (Physical Chem)

Question 1

What is the Symbol for Enthalpy

Answer 1

ΔHof

Question 2

What is the standard enthalpy of formation

Answer 2

The standard enthalpy of formation ΔHof is the enthalpy change when one mole of a substance is formed from its elements in their standard states.

Question 3

When is the standard state of a substance most stable?

Answer 3

At a pressure of 1 atmosphere and at a temperature of 298K.

Question 4

The standard enthalpy of a reaction Equation

Answer 4

ΔHo (reaction) = ΣΔHof (products) - ΣΔHof (reactants)

Question 5

What is the Enthalpy of Sublimation

Answer 5

The energy required to convert one mole of a solid element into separate atoms in the gas state. The most common one we use is carbon.

Question 6

What is the symbol for entropy

Answer 6

S

Question 7

What is entropy

Answer 7

The entropy (S) of a system is a measure of the degree of disorder of the system.

Question 8

The greater the degree of disorder

Answer 8

the greater the entropy.

Question 9

Talk about entropy in terms of solids, gasses and temperature

Answer 9

Solids have low disorder

gases have high disorder

Entropy increases as temperature increases.

Question 10

How does the entropy change as it reaches the melting and boiling points

Answer 10

rapid increase for m.p. and even more rapid increase for b.p.

Question 11

What is the 3rd Law of thermodynamics?

And why is it so?

Answer 11

the entropy of a perfect crystal at 0 K is zero.

This is because the particles in a solid at 0 K are perfectly ordered an no longer vibrating.

Question 12

What is the standard entropy of a substance (So)

Answer 12

the entropy of 1 mol of the substance at a pressure of 1 atmosphere at room temperature (usually 298K).

Question 13

Units of Entropy

Answer 13

J K^ -1 mol^ -1

Question 14

Describe the relationship between entropy and ΔSo (Get explained)

Answer 14

For increase in entropy ΔSo will have a positive value, whereas a decrease in entropy ΔSo will give a negative value.

Question 15

When is a reaction spontaneous or feasible?

Answer 15

if it tends to occur in the forward direction. (ΔSo is positive)

Question 16

2nd Law of thermodynamics

Answer 16

The total entropy of a reaction system and its surroundings always increases for a spontaneous process.

Question 17

How does Heat energy released by the reaction system affect the surroundings?

Answer 17

increases the entropy of the surroundings.

Question 18

How does Heat energy absorbed by the reaction system affect the surroundings?

Answer 18

decreases the entropy of the surroundings.

Question 19

Equation to calculate change in standard entropy for a reaction system

Answer 19

Δ So (reaction) = ΣSo (products) - ΣSo (reactants)

Question 20

Standard free energy symbol

Answer 20

G^o

Question 21

The standard free energy change equation

Answer 21

ΔGo = ΔHo - TΔSo

Question 22

For a reaction to be feasible ΔGo must be…..

Answer 22

negative.

Question 23

At equilibrium ΔG = ?

Answer 23

0

Question 24

What values are observed to estimate The temperature at which a reaction may be feasible

Answer 24

range of values for T for which ΔGo is negative in the equation:

ΔGo = ΔHo - TΔSo

Question 25

The standard free energy change, ΔGo for a reaction can be calculated using the equation….

Answer 25

ΔGo (reaction) = ΣGo (products) - ΣGo (reactants)

Question 26

The standard free energy of formation of an element (in its most stable form) is…..

Answer 26

0