Using & Controlling Reactions: Equilibrium

Question 1

Reversible Reactions

Answer 1

most chemical reactions are reversible ie.
forward reaction = R ->P
back reaction = R <- P

Question 2

Reversible Reactions…Equilibrium

Answer 2

the concentrations of products & reactants in a reversible reaction will eventually reach constant values if:

• in a closed system (no loss/gain of total mass of reactants/products)
• at a constant temperature

Question 3

Equilibrium

Answer 3

• dynamic (not static)
• forward & back reactions occur at equal rates
• measurable/observable properties are constant (eg. pH, colour, pressure)

Question 4

Equilibrium Constant Kc

Answer 4

= indicates the position of equilibrium at a given temperature (related to [reactants] and [products])

• indicates the equilibrium yield of products relative to quantities of reactions (the extent of a reaction)
• large Kc > 10 = high yield of products
• low Kc < 0.1 = low yield of products

Question 5

Le Chatelier’s Principle

Answer 5

= if a change is made to a system at equilibrium, the system will react to counteract that change

• the extent of a reversible reaction may be changed by altering reaction conditions: concentration, pressure, temperature
• important in industrial chemistry - yield of product

Question 6

Le Chatelier’s Principle - Concentration

Answer 6

= changed by addition/removal of reactants/products
increase R = eqm moves to P
decrease R = eqm moves to R
increase product = eqm moves to R
decrease product = eqm moves to P

Question 7

Le Chatelier’s Principle - Pressure

Answer 7

= changed by altering the volume of the reaction vessel
increase pressure (by decreasing volume) = eqm moves to side with less molecules
decrease pressure (by increasing volume) = eqm moves to side with more molecules

Question 8

Le Chatelier’s Principle (Explanation)

Answer 8

… if we increase the concentration of reactant, we have upset the equilibrium & so according to Le Chatelier’s Principle, the system to react to try to counteract the change. The equilibrium will push to the right (more product) to remove the excess reactant.

Question 9

Le Chatelier’s Principle - Temperature

Answer 9

= change in temperature, equilibrium shifts in the direction of endothermic/exothermic reaction to absorb/replace energy
increase temperature = eqm moves to endothermic side
decrease temperature = eqm moves to exothermic side