Read Equilibrium Shifts Before Predicting Yield
Equilibrium-position questions reduce to identifying which direction Le Chatelier's principle pushes the reaction, then confirming that direction matches whatever Kc/Kp calculation the numbers actually demand.
Chemistry questions first require the material, particles or reaction condition to be identified before a formula or rule is selected.
Reading a yield-vs-temperature graph at two pressures
If product yield falls as temperature rises, the forward reaction is exothermic. Comparing the same reaction at two different total pressures separates out whether increasing pressure favours the side with fewer gas moles — read both effects off the graph independently before combining them into one answer.
Computing Kc from a mass or mole ratio at equilibrium
Convert whatever ratio is given (mass ratio, mole ratio) into moles of each species using molar mass, then substitute into the Kc expression with the correct stoichiometric powers — a mass ratio is not directly usable in Kc without this conversion step.
Gibbs energy as the real criterion for spontaneity
ΔG, not ΔH or ΔS alone, decides whether a process is spontaneous at a given temperature — a reaction can have unfavourable ΔH and still be spontaneous if TΔS is large enough, and vice versa.
OlympIQ exam lens
- ✓Yield falling as temperature rises means the forward reaction is exothermic.
- ✓Increasing pressure favours whichever side has fewer moles of gas.
- ✓Convert mass or other given ratios into mole ratios before substituting into Kc — it needs concentrations, not raw masses.
- ✓ΔG determines spontaneity, not ΔH or ΔS in isolation.
Don't read a yield-vs-temperature graph and a yield-vs-pressure comparison as the same shift — temperature tells you the sign of ΔH, pressure tells you which side has fewer gas moles; keep them as two separate deductions.
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