Stoichiometric and ICE-Table Equilibrium Calculations

All flashcards

ICE table

A table organizing initial concentrations, stoichiometric changes, and equilibrium concentrations.

Equilibrium concentration

The initial concentration plus the reaction-driven change for that species.

Equilibrium-constant exponents

In a concentration equilibrium expression, each exponent comes from the species' balanced-equation coefficient.

Reaction quotient comparison

Comparing $Q_c$ with $K_c$ identifies the direction of net reaction.

Small-change approximation

An approximation replacing an initial concentration minus $x$ with the initial concentration when $x$ is much smaller.

Quiz questions

1. For a reaction at fixed conditions, what does $Q_c>K_c$ indicate?Answer: The reaction proceeds in reverse to approach equilibrium.
2. What is the $K_c$ expression for $PCl_5(g) \rightleftharpoons PCl_3(g)+Cl_2(g)$?Answer: $K_c=\frac{[PCl_3][Cl_2]}{[PCl_5]}$
3. For $N_2(g)+O_2(g)\rightleftharpoons 2NO(g)$, how can $[NO]$ be found from known $K_c$, $[N_2]$, and $[O_2]$?Answer: $[NO]=\sqrt{K_c[N_2][O_2]}$
4. When calculating $K_c$ from a reaction mixture, which concentrations should be substituted?Answer: The species' concentrations at equilibrium.
5. A quadratic equation for an ICE-table change variable gives one positive root and one negative root. Why should a negative root be rejected when it implies a negative species concentration?Answer: A concentration cannot be negative in the stated physical system.