Enthalpy and Entropy Flashcards
What is entropy?
A measure of the dispersal of energy in a system, which is greater the more disordered a system is.
How can entropy be calculated qulitatively?
By looking at how many ways things can be organised (gas = more entropy because more disorderd) as well as how much of each substance we have (3 mol gas is more disordered than 2 mol gas)
List liquid, solid and gas in order of increasing entropy/disorderdness.
Solid, liquid, gas. Because the particles can be in may more positions gaseous state than solid state.
Why is entropy important?
To decide the feasibility of a reaction using Gibb’s free energy equation.
What does a Gibbs free energy of less than 0 mean?
The reaction is feasible
What is the Gibbs free energy equation?
ΔG° = ΔH° - TΔS°
ΔG° = change in Gibbs free energy (KJmol-1)
ΔH° = change in enthalpy (KJmol-1)
T = absolute temperature (in K)
ΔS° = entropy change of a reaction (JK-1mol-1)
How to caltulate entropy?
(GIVEN TO YOU) entropy of products - entropy of reactants. If the products have more entropy than the reactants, we have a positive entropy change (more disordered)
What affects the feasibility of a reaction?
Temperature, entropy change and enthalpy change. TΔS° needs to be less negative (bigger) than change in enthalpy for the reaction to be feasible.
How do you find the temperature at which a reaction stops becoming feasible.
Set ΔG to 0 and rearrange for T. Make sure to substitute all known values and have entropy in KJ by dividing it by 1000.
Why does a very high temperature decrease feasibility of a reaction?
Because if entropy is negative, T delta S is now more negative than delta H, so Gibbs free energy will be greater than 0.
What is the limitation of Gibbs free energy?
Delta G being less than 0 doesn’t confirm if a reaction will actually happen. This is because its not the only thing that affects a reaction. Eg, a really low rate of reaction. The reaction won’t happen even if delta g is negative.
