Download Chemical Equilibrium

Chemical Equilibrium
AUTHOR: WESLEY TUNG
Technical Things
A chemical equation of a reaction uses mole ratios to
describe the production of products from reactants.
◦ In 2𝐻2 + 𝑂2 → 2𝐻2 𝑂, hydrogen and oxygen are reactants, and
water is a product.
◦ This equation has a 2:1:1 mole ratio.
1 mole contains 6.022 × 1023 molecules/atoms.
◦ This is also known as Avogadro's number.
Intro to Equilibrium
History
◦ In 1803, Claude Louis Berthelot, a Savoyard-French chemist, discovered some chemical reactions
were reversible.
Definition of Equilibrium
◦ The state in a chemical reaction in which both products and reactants are present in concentrations
that have no further tendency to change over time.
Two types of chemical equilibrium exist:
◦ Static Equilibrium
◦ The reaction is irreversible.
◦ Dynamic Equilibrium
◦ The reaction is reversible.
Reaction Quotient
The reaction quotient is a constant that tell us the ratio of products
to reactants at a specific state in the reaction.
◦ For a reaction 𝑎𝐴 + 𝑏𝐵 ↔ 𝑐𝐶 + 𝑑𝐷 , the reaction quotient (𝑄𝑐 ) is
calculated by:
[𝐶]𝑐 [𝐷]𝑑
◦ 𝑎 𝑏
[𝐴] 𝐵
= 𝑄𝑐
◦ Brackets stand for concentration in molarity.
◦ Molarity (M) =
𝑚𝑜𝑙𝑒𝑠 𝑜𝑓 𝑠𝑢𝑏𝑠𝑡𝑎𝑛𝑐𝑒
𝐿𝑖𝑡𝑒𝑟𝑠
◦ Only gaseous and aqueous compounds are included in the equation.
Equilibrium Constant
The equilibrium constant is the reaction quotient value for a system when it is in
it’s equilibrium state.
Every system of equilibrium has a unique equilibrium constant (K) that is
determined experimentally initially.
◦ To do this, you must let the reaction run to its equilibrium state, then figure out the
concentrations of each component.
◦ This constant allows us to determine whether the same system under different conditions is
at equilibrium.
◦ When 𝑄𝑐 = 𝐾 the system is at equilibrium.
◦ When 𝑄𝑐 ≠ 𝐾, the system is not at equilibrium and will produce more products or reactants to achieve
equilibrium.
Le Chatelier's Principle
History
◦ Developed by Henry-Louis Le Chatelier in 1884 to predict the change in
disturbed equilibrium systems to re-achieve equilibrium.
◦ In general:
◦ Increasing the concentration of reactants causes more products to be made (Shift right).
◦ Increasing the concentration of products causes more reactants to be made (Shift left).
◦ Decreasing the volume but keeping everything else constant would shift the reaction towards the
side of the reaction that produces the least total amount of moles.
◦ Increasing the volume but keeping everything constant would shift the reaction towards the side of
the reaction that produces the most amount of moles.
Le Chatelier’s Principle
Temperature is unique
◦ It doesn’t modify the reactant quotient like volume and concentration but
modifies the equilibrium constant.
◦ The shift depends on whether the reaction is exothermic or endothermic:
◦ Endothermic: Heat is a reactant and the reaction shifts right if you increase the temperature.
◦ Exothermic: Heat is a product and the reaction shifts left if you increase the temperature.