5.2.2 - (a-f)

Question 1

Define entropy

Answer 1

Entropy, S:

A measure of dispersal of energy and how disordered a chemical system is

• Unit is usually J
• Entropy increases as dispersal increases or a chemical system becomes more disordered

Question 2

How doe entropy change from solid to gas?

Answer 2

• Entropy incrases as there is an opportunity for energy to be spread
• MP/BP increases randomness of particles

Question 3

How does entropy change when there is a change in the n^o of gaseous molecules?

Answer 3

• Reactions producing gases increase entropy
  
  • ​Because, particles become more disordered
  • Energy is more spread, so entropy change is +ve

N_2(g) + 3H_2(g) → 2NH_3(g)

• Decrease in particle randomness
• Energy is less spread as the reaction goes from 4 moles of gas to 2
• Therefore, entropy change is negative

Question 4

Define standard entropy

How do you calculate entropy change?

Answer 4

Standard Entropy: Entropy of 1 mol of a substance under standard conditions (100kPA and 298K)

• Units JK^-1mol^-1
• Always positive

Question 5

What is the feasability of a reaction?

Answer 5

How likely a reaction is to occur based on whether it is energetically feasible (spotaneous) or not, based on free energy change

Question 6

What is free energy change?

Answer 6

• Overall change in energy during a chemical reaction, based on 2 energies
  
  • Enthalpy change: Heat transfer between system and surroundings
  • Temp.Entropy Change: Entropy change at a given temperature of a reactiom

Question 7

What is Gibbs Equation?

Answer 7

• Calculation for free energy
• A reaction is feasible if G<0
• NOTE: For entropy change, convert to kJmol^-1K^-1 as it is usually given in Jmol^-1K^-1

Question 8

What are the limitations of Gibbs’ Free Energy Equations?

Answer 8

• Does not take into accuont kinetics or reaction rate
• A reaction may be feasible based on G, but the activation energy may be too high and stops the reaction from occuring