Thermodynamics

Question 1

Give the equation for entropy change (Δ S)

Answer 1

Entropy of products - reactants

Question 2

ΔG =

Answer 2

ΔH - T ΔS
Enthalpy change - temp x entropy

Question 3

Entropy is a measure of what ?

Answer 3

Disorder

Question 4

Give a definition of enthalpy of formation

Answer 4

The enthalpy change when one mole of a compound is formed and reactants are in their standard states

Question 5

Define enthalpy of combustion

Answer 5

The enthalpy change when one mole of a compound is completely burned in oxygen

Question 6

Define enthalpy of atomisation

Answer 6

The enthalpy change when one mole of gaseous ions is formed from an element in its standard state

Question 7

Define bond enthalpy

Answer 7

The enthalpy change when one mole of gaseous molecules break a covalent bond to form two atoms

Question 8

Define electron affinity

Answer 8

The enthalpy change when when one mole of gaseous ions is converted into a mole of gaseous ions with a negative charge

Question 9

Define lattice enthalpy

Answer 9

The enthalpy change when one mole of a solid ionic compound is formed from its gaseous ions

Question 10

When ΔH is positive and ΔS is positive is the reaction feasible (and why)

Answer 10

The t ΔS is negative ,so subtracted from ΔH , so t ΔS must be greater than ΔH in order for ΔG to be negative
Only feasible at high temperatures

Question 11

When ΔH is negative and ΔS is negative is the reaction feasible (and why)

Answer 11

T ΔS is now positive ,so is added to ΔH
Therefore this reaction is only feasible when t ΔS is less than ΔH
Therefore only feasible at low temperatures

Question 12

When ΔH is positive and ΔS is negative is the reaction feasible (and why)

Answer 12

The t ΔS is now positive,so added to ΔH
This means the reaction is never feasible as ΔG is always positive