[22.5] free energy Flashcards
1
Q
what is a feasible reaction?
A
a reaction that is able to happen and is thermodynamically possible
2
Q
what is the free energy change ΔG?
A
the overall change in energy during a chemical reaction
3
Q
what conditions are favoured in feasible reactions?
A
- lower energy state - exothermic reactions (enthalpy change ΔH is negative
- increasing disorder is energetically favoured (entropy change ΔS is positive)
4
Q
what are the two types of energy which make ΔG?
A
- enthalpy change ΔH
- entropy change at the temperature of the reaction TΔS (this is the dispersal of energy within the chemical reaction itself)
5
Q
what is gibbs’ equation?
A
ΔG = ΔH - TΔS
6
Q
describe the individuals components of gibbs’ equation
A
- ΔG = free energy change (kJ mol⁻¹)
- ΔH = enthalpy change (kJ mol⁻¹)
- T = temperature (K)
- ΔS = entropy change of system, may be given in joules but convert to kJ (kJ K⁻¹ mol⁻¹)
7
Q
how do you know if a reaction is feasible based on the ΔG value?
A
a negative ΔG value means the reaction is feasible
8
Q
why might a reaction that is feasible not take place ‘spontaneously’?
A
- due to having a very high activation energy
- a reaction will not take place until you first overcome the activation energy
9
Q
at what point does a reaction switch from being feasible to not feasible?
A
- when ΔG = 0
- feasibility can change with temperature in some cases
10
Q
how do you calculate the temperature (K) at which feasibility changes?
A
T = ΔH / ΔS
11
Q
gibbs’ equation and graphs
A
- ‘ΔG = ΔH - TΔS’ is linked to ‘y = mx + c’ on a graph
- ΔG = y axis, T = x axis
- gradient = -ΔS
- y axis intercept = ΔH
- x axis intercept = temperature when reaction becomes unfeasible
