unit 7 chemistry

Equilibrium

• Physical is a reversible change of state.

• Chemical is a reversible chemical reaction that can go in the direction to create products or to create reactants.

rate of the forward reaction is the same as the rate of the reverse reaction.

Key info

• Only achieved in closed systems

• Only possible in reversible reactions

• dynamic because because the forward and reverse reactions are continuously happening at the same time and the same rate.

• NOT same amount of products and reactants

• No net change in reactants and products when reaching

Concentration graph at equilibrium

amount of product and reactant remains constant

reaction graph at equilibrium

Proceed at same rate (foward and reverse)

Reaction Quotient (Q)

relative concentration/pressure of the reaction species at any time

Equilibrium Constant (K)

relative concentration/pressure of reaction species at equilibrium.

Equilibrium Expressions

Keq= [Concentration products] / [reactants] (no solids or liquids)

Reverse: More reactants formed

Foward: More products formed

When Keq> 1, reaction is product favored

When Keq< 1, reactant favored

When Keq very small, heavily reactant favored

When Keq very large, heavily product favored

Aqueous (concetration)

Qc + Kc

Gases (pressure)

Qp + Kp

A + B - C + D

Increase in concentration: shift AWAY from the side of the reaction where the substance is found

Decrease in concentration: shift TOWARDS the side of the reaction where the substance is found

Increase temperature: Shift away from the heat source

Decreased temperature: Shift rowards the heat

Increased pressure: Shift away from the side with the largest cumulative number of molecules found (coefficients)

Decreased pressure: Shift towards the side with the largest cumulative number of molecules found (coefficients)

Endothermic: Heat is a reactant

Exothermic: Heat is a product

When a stress is applied to a system in dynamic equilibrium, Q is no longer equal to K.

• A shift occurs so Q is again equal to K.

Calculating K with multistep

When flipping the reaction, take the inverse

When doubling the reaction, square it

ICE

Initial, concentration, equilibrium

K_sp Calculations

• Ksp is not the same as solubility.

• Solubility is the quantity of a substance that dissolves to form a saturated solution

• Molar solubility (s): The moles of solute that can dissolve in 1L of solvent 

  • Units mol/L or M

• Common units for solubility: Grams per liter (g/L) or Moles per liter (mol/L)