Approaching Equilibrium Lesson 1

Approaching Equilibrium   Many chemical reactions are reversible if the activation energy is low. Reactants ⇌ Products

Approaching Equilibrium   Many chemical reactions are reversible if the activation energy is low. Reactants ⇌ Products Always on left Always on right   

Approaching Equilibrium   Many chemical reactions are reversible if the activation energy is low. Reactants ⇌ Products

Approaching Equilibrium   Many chemical reactions are reversible if the activation energy is low. Reactants ⇌ Products Forward Rate is from left to right  

Approaching Equilibrium   Many chemical reactions are reversible if the activation energy is low. Reactants ⇌ Products Reverse Rate is from right to left  

Lets see what happens to some reactants if they are placed in a reaction vessel and allowed to react.  

Approaching Equilibrium Reactants Products Forward Rate Reverse Rate

Approaching Equilibrium Reactants Products Forward Rate Reverse Rate

Approaching Equilibrium Reactants Products Forward Rate Reverse Rate

Approaching Equilibrium Reactants Products Forward Rate Reverse Rate

Approaching Equilibrium Reactants Products Forward Rate Reverse Rate

Approaching Equilibrium Reactants Products Forward Rate Reverse Rate

Approaching Equilibrium Reactants Products Forward Rate Reverse Rate

Approaching Equilibrium Reactants Products Forward Rate Reverse Rate Are Equal

Approaching Equilibrium Reactants Products Forward Rate Reverse Rate Are Equal Are Constant

Time [Reactant] Forward Rate [Product] Reverse Rate Net Rate   0 8000 170 0 0 170 5 7500 160 1000 16 144 10 6800 145 2000 20 120 15  5600 120 2500 30 90 20 4600 100 3200 40 60 25 3600 84 4000 50 34 30 2900 75 4900 56 19 35 2000 65 6000 58 7 40 1600 60 6000 60 0 45 1600 60 6000 60 0 50 1600 60 6000 60 0

Equilibrium has been attained after 40 minutes Equilibrium has been attained after 40 minutes. The forward and reverse rates are equal and the reactant and product concentrations are constant.

Graph the [reactant] and [product] as equilibrium is approached.    Concentration   8000 7000    6000 5000   4000 3000 2000 1000 0 15 30 Time   equilibrium

Graph the forward, reverse, & net rates as equilibrium is approached.   160   140    120 100   80 60 40 20 0 15 30 Time   equilibrium

Approaching Equilibrium Reactant concentrations start high and decrease as the reaction proceeds. The forward rate, which depends on collisions of the reactants, also decreases.   Product concentrations start at zero and increase as the reaction proceeds. The reverse rate, which depends on collisions of the products, also increases. Eventually the forward rate is equal to the reverse rate and the concentrations are constant. This is equilibrium.

Characteristics of a System at Equilibrium   The Forward rate = The Reverse rate The Reactant and Product concentrations are constant The Macroscopic (observable) properties are constant The system is Dynamic as the forward and reverse reactions continue. The equilibrium can be approached from starting with reactants or starting with products.

Conditions Necessary for Equilibrium   The system is closed. The temperature is constant. The Ea is low enough so that the reaction is reversible. Simulation1