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Flashcards in 5.2.2 - (a-f) Deck (8)
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Define entropy

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


How doe entropy change from solid to gas?

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


How does entropy change when there is a change in the no of gaseous molecules?

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

N2(g) + 3H2(g) → 2NH3(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


Define standard entropy

How do you calculate entropy change?

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

  • Units JK-1mol-1
  • Always positive



What is the feasability of a reaction?

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


What is free energy change?

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


What is Gibbs Equation?

  • 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


What are the limitations of Gibbs' Free Energy Equations?

  • 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