Entropy
This term measures the dispersal or distribution of matter and energy in a system.
(What is?) Entropy
The equation that relates Gibbs free energy change (ΔG) to enthalpy (ΔH), entropy (ΔS), and temperature (T) is:
(What is?) ΔG = ΔH − TΔS?
At constant pressure, a reaction is spontaneous if ΔG is:
(What is?) negative (ΔG < 0)?
As a reaction approaches equilibrium, ΔG becomes less negative. What value does ΔG have at equilibrium?
(What is?) ΔG = 0?
Rank these states of matter in order of increasing entropy: gas, liquid, solid.
(What is?) solid < liquid < gas?
If a reaction has ΔH = −20 kJ/mol and ΔS = −50 J/mol·K at 298 K, calculate ΔG and determine spontaneity.
(What is?) −5,100 J/mol (spontaneous)
Give an example of a reaction that is non-spontaneous at low temperatures but spontaneous at high temperatures. Explain why.
(What is?) the dissolution of NH4NO3 in water; ΔH > 0 and ΔS > 0, so TΔS must be large enough for ΔG to become negative?
Explain the relationship between ΔG, Q (reaction quotient), and K (equilibrium constant) for a reaction at any point before equilibrium.
(What is?) ΔG = ΔG° + RT ln Q; when Q < K, ΔG < 0 and the reaction is spontaneous in the forward direction; when Q > K, ΔG > 0 and the reaction is non-spontaneous forward?
Explain why the dissolution of a solid salt in water generally increases the entropy of the system.
(What is?) because ions are dispersed in solution, increasing the number of ways energy and particles are distributed?
A reaction has ΔG = 0 at a certain temperature. Explain what this implies about the reaction.
(What is?) the reaction is at equilibrium, and no net change occurs in the forward or reverse direction?