Equilibrium Connections

Big picture: how do K, Q, and ΔG fit together?

K describes the balance point. Q describes where you are right now. ΔG tells which way you will move next. At equilibrium: Q = K and ΔG = 0.

What changes K vs what changes Q?

K changes only with temperature. Q changes when you change concentrations, partial pressures, or volume.

How do you decide shift using Q compared to K?

Q < K means make products. Q > K means make reactants. Q = K means no net change.

How does Le Châtelier connect to Q and K?

Every stress that changes concentrations or pressure changes Q. The system then shifts until Q returns to K.

Why do solids and pure liquids not appear in Q or K?

Their activities are constant. Changing the amount of a pure solid or liquid does not change Q or K.

What does temperature do in plain terms?

Temperature changes K by favoring the endothermic direction when T increases and the exothermic direction when T decreases.

How do exothermic reactions respond to higher temperature?

Heat acts like a product. Higher T pushes equilibrium left. K gets smaller.

How do endothermic reactions respond to higher temperature?

Heat acts like a reactant. Higher T pushes equilibrium right. K gets larger.

How does volume change connect to Q for gas equilibria?

Lower volume raises total pressure. Q changes so the system favors the side with fewer gas moles. Higher volume does the opposite.

Does adding an inert gas at constant volume shift equilibrium? Why?

No. Partial pressures of reacting gases are unchanged, so Q does not change.

Does adding an inert gas at constant pressure shift equilibrium? Why?

Yes. Volume must increase to hold pressure constant, which changes concentrations and shifts toward the side with more gas moles.

How do catalysts fit into the picture?

They lower activation energy and speed the approach to equilibrium. They do not change K, Q at equilibrium, or the final composition.

How do rate ideas connect to equilibrium ideas?

At equilibrium forward rate equals reverse rate. K does not come from speed. It comes from the ratio of concentrations at that balance point.

What does K tell you about composition, not speed?

Large K means product heavy at equilibrium. Small K means reactant heavy. K says nothing about how fast you get there.

How does ΔG° connect to K?

ΔG° = −RT ln K. If K > 1 then ΔG° < 0 and products are favored at standard conditions. If K < 1 then ΔG° > 0 and reactants are favored.

How does nonstandard ΔG connect to where the system goes next?

Use the sign of ΔG. ΔG < 0 means the forward move is favorable at the current mix. ΔG > 0 means the reverse move is favorable.

How do you translate "shift right" into what actually happens in the beaker?

Reactants get used. Products form. The system continues until Q again equals K.

How do you translate "shift left" into what actually happens in the beaker?

Products get used. Reactants form. The system continues until Q again equals K.

What is the role of a RICE table in this map?

It turns the qualitative shift into numbers by tracking Initial, Change, and Equilibrium so you can enforce Q = K at the end.

When is the small-x idea conceptually valid?

When the shift is tiny compared to what you started with, the equilibrium point is close to the initial point.

How can you predict the sign of the first change without math?

Compare Q to K. If Q < K, products must increase first. If Q > K, reactants must increase first.

How does removing a product tie together with Q and Le Châtelier?

Removing product makes Q smaller. Q < K so the system makes more product until Q = K again.

How do standard vs nonstandard conditions connect across topics?

Standard gives ΔG° and K. Real mixtures are nonstandard so you use Q and ΔG to see the direction toward the same K at that temperature.

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