There are several factors affect reaction rates ◦ Concentration ◦ Surface area (Particle size) ◦ Temperature ◦ Catalysts ◦ Inhibitors
A catalyst is a substance that increases the rate of a chemical reaction without itself being used up in the reaction. A catalysts provide an alternative energy pathway for the reaction. The different pathway lowers the activation energy allowing more molecules to overcome the activation energy and produce products at a faster rate
HH A lower activation energy allows more molecules to overcome the activation energy, speeding up the reaction Potential Energy
An inhibitor is a substance that slows down, or inhibits reaction rates. Uses ◦ A preservative ◦ A weed killer
When a reaction results in complete conversion of reactants to products chemists say it goes to completion Not all reactions go to completion. They appear to stop because they are reversible Reversible reactions can occur in both the forward and reverse directions
Forward N 2 + 3H 2 2NH 3 ◦ The reactants are N 2 and H 2 Reverse N 2 + 3H 2 2NH 3 ◦ The reactant is NH 3 N 2 + 3H 2 ⇆ 2NH 3 The forward and reverse reactions are happening at the same time.
Chemical equilibrium is a state in which the forward and reverse reactions balance each other because they take place at equal rates. ◦ Rate forward reaction = Rate reverse reaction This does not mean the concentrations of the products and reactants are the same Equilibrium is a state of action, not inaction. This process is dynamic; dynamic equilibrium.
uU6A uU6A
Law of chemical equilibrium states that at a given temperature, a chemical system may reach a state in which a particular ratio of reactant and product concentrations has a constant value known as Keq or equilibrium constant.
Keq is the ratio of product concentrations to reactant concentrations. A large Keq, Keq > 1 means the products are favored over the reactants A small Keq, Keq < 1 means the reactants are favored over the products
Homogenous equilibrium means all reactants and products are in the same physical state Ex: H 2 (g) + O 2 (g) H 2 0(g) Heterogeneous equilibrium is when the reactants and products are in more than one physical state. Ex: H 2 O(g) + C(s) H 2 (g) + CO(g)
aA + bB cC +dD products [C] c [D] d reactants [A] a [B] b == K eq **only use K eq for gases and aqueous compounds
1. Given N 2 (g) + 3H 2 (g) 2NH 3 (g) write the equilibrium constant expression for the reaction.
2. Given SO 2 (g) + O 2 (g) 2SO 3 (g) write the equilibrium constant expression for the reaction.
1. Given 2NaHCO 3 (s) Na 2 CO 3 (s) + CO 2 (g) + 3H 2 O (g) write the equilibrium constant expression for the reaction.
At equilibrium and 100°C a flask contains: [PCl 5 ]=0.0325M[H 2 O]=0.025M [HCl]=0.375M[POCl 3 ]=0.250M Calculate the K eq for the reaction PCl 5 (g) + H 2 0 (g) 2HCl (g) + POCl 3 (g)