Ch 16: Chemical Equilibrium

What does it mean for a process to be reversible?

The products of the reaction can react to form reactants

In regard to the rate, what does it mean for a system to be in equilibrium?

The rates of the forward reaction and reverse reaction are the same

What does it mean when we say equilibrium is a "dynamic state"?

Both forward and reverse reactions continue to occur, but there's no net change in reactant or product concentrations over time.

True or False: At equilibrium, chemical reactions stop occurring.

False. Reactions continue in both directions, but concentrations remain constant.

What remains unchanged at equilibrium?

The concentrations of reactants and products.

In what ways can equilibrium be established?

Starting with only reactants, only products, or any mixture of both.

True or False: Equilibrium can only be reached if both reactants and products are present initially.

False. It can be reached from reactants only, products only, or a mix.

What is the reaction quotient?

• Q_c = a fraction with product concentrations in the numerator and reactant concentrations in the denominator 

  • each conc. is raised to a power = to its stoichiometric coefficient in the balanced chemical equation

What is the law of mass action?

the rate of a chemical reaction is directly proportional to the product of the concentrations of the reactants, each raised to the power of their respective stoichiometric coefficients.

What is the equilibrium constant?

• K_c  = (Conc of product/s raised to stoichiometric coefficient)/(Conc of reactant/s raised to stoichiometric coefficient)

What is the reaction quotient of Ag⁺(aq) + 2NH₃(aq)to Ag(NH₃)₂⁺(aq)?

What is the reaction quotient for N₂(𝑔) + 3H₂(g) ⇄ 2NH₃(𝑔)?

*if we were using partial pressure (atm): Q_c = (P_NH3)²/(P_N2)(P_H2)³ where P = pressure

If K_c > 1 then _____ are favored

If K_c < 1 then _____ are favored

• Products are favored; there are more products present 

• Reactants are favored; there are more reactants present

When is it better to use Q_c vs K_c?

• Only use K_c when the system is at equilibrium

• Q_c is used when the system is not known to be at equilibrium

What does it mean for a chemical reaction to be heterogeneous?

• When the species in a reversible chemical reaction are not all in the same phase

  • ie some are gas, some are solid, etc.

If you are asked to find the K_c of a heterogeneous reaction, what are the rules you need to follow?

• Only gas and aqueous appear in equilibrium

• Pure solids and pure liquids do NOT appear in  equilibrium

(True/False): Reversing a chemical equation inverts the equilibrium constant.

True, og K_c becomes 1/K_c

What is the new equilibrium constant for:
2C(g) to A(g) + B(g) if the original is A(g) + B(g) to 2C(g0