ICE tables

How do you decide if a system is at equilibrium using K and current concentrations?

Compute Q in the same form as K. If Q < K, it shifts right (makes products). If Q > K, it shifts left (makes reactants). If Q = K, it is at equilibrium.

What does RICE stand for in equilibrium problems?

Reaction, Initial, Change, Equilibrium.

Why use a RICE table?

To track how each species changes from initial to equilibrium so you can plug equilibrium concentrations into K.

In a RICE table, how do you decide the signs in the Change row?

Negative for species that are consumed; positive for species that are produced. Use stoichiometric ratios for the magnitudes.

Steps to find equilibrium concentrations when K and initial concentrations are given?

1) Compute Q to predict shift. 2) Set up a RICE table with x. 3) Write K in terms of x. 4) Solve for x. 5) Calculate equilibrium concentrations.

If the reaction starts with only reactants, what does Q equal at t = 0?

Q = 0 (as long as products start at 0).

How do you convert moles to molarity for a RICE table?

M = n/V, with V in liters.

What is the Rule of 100 for simplifying equilibrium calculations?

If 100 × K is less than the relevant initial concentration, you can often assume x is small and drop it from sums like (C0 − x) ≈ C0.

When can you use the small‑x approximation?

When K is small and initial reactant concentrations are relatively large, so the change x is small compared to the initial values.

How do you check if the small‑x assumption was valid after solving?

Compare x to the initial concentration. If x is much smaller, the assumption is acceptable.

For aA + bB ⇌ cC + dD, what is the general K_c expression?

K_c = [C]^c [D]^d / ([A]^a [B]^b).

What species are excluded from K_c and Q_c expressions?

Pure solids and pure liquids are omitted.

What does it mean for the reaction to shift right in these problems?

Products increase and reactants decrease until a new equilibrium is reached.

What does it mean for the reaction to shift left in these problems?

Reactants increase and products decrease until a new equilibrium is reached.

When you are given one equilibrium concentration, how do you use it?

Use it to find x from the RICE table, then apply stoichiometry to get all other equilibrium concentrations.

If K_c is given at a temperature, can you use it at another temperature?

No. K depends on temperature. Use the value given for that temperature.