Chemistry ✿ the rate and extent of chemical change

equation for mean rate of reaction

total amount of products/ reactants (g or cm³) / time taken (s)

dm³ → cm³

multiply by 1000

what 4 conditions can increase the rate of reaction?

how does higher temperatures increase the rate?

• increase surface area

• high temperature

• high concentration

• high pressure

more kinetic energy causes more successful collisions

why do smaller objects such as powders increase the rate of reaction?

• have a larger surface area to volume ratio,

• so more collisions of particles take place

collision theory

chemical reactions can only occur when particles collide with enough energy

activation energy

the minimum amount of energy used by particles so they react

catalyst

substances which increase rate of chemical reaction by providing an alternative reaction pathway with a lower activation energy

how can the student investigate how the rate of reaction when the concentration of is changed by measuring the volume of gas produced?

• use 50cm³ of 1mol/dm³ hydrochloric acid

• use 3cm magnesium ribbon

• set up a conical flask containing 50cm³ of 1mol/dm³ hydrochloric acid

• have bung and delivery tube attached to gas syringe prepared

• add a 3cm piece of magnesium ribbon

• quickly fit bung on conical flask and start a stopwatch

• record the measurement of gas produced every 10 seconds

• repeat experiment with 2 and 3 mol/dm³ hydrochloric acid

how can the student investigate how the rate of reaction when the concentration of is changed by observing change of colour or turbidity?

• use 10cm³ sodium thiosulfate solution

• use 10cm³ dilute hydrochloric acid

• pour 10cm³ of sodium thiosulfate solution into a conical flask

• measure out 40cm³ water with a measuring cylinder and pour into conical flask

• add 10cm³ dilute hydrochloric acid into conical flask and place it on a black cross and start a stopwatch

• record the time it takes for the cross to disappear

• repeat using other concentrations of sodium thiosulfate

reversible reaction

a reaction were the products can also form the reactants. If one direction is exothermic, the other one is always endothermic

exothermic

transfers energy to the surroundings

endothermic

takes in energy from surrounding

equilibrium

when the forward and backward reaction in a reversible reaction happen at the same rate in a sealed container

le chatelier’s principle

when a change of conditions happens to a system at equilibrium, the position of equilibrium moves to cancel out the change

If the concentration of a system at equilibrium is increased, what happens to the equilibrium?

• equilibrium shifts to opposite side of substance which has increased concentration

If the concentration of a system at equilibrium is decreased, what happens to the equilibrium?

• equilibrium shifts to the side of substance which has decreased concentration

(for gaseous reactions)
If the pressure of a system at equilibrium is increased, what happens to the equilibrium?

• the equilibrium position will shift towards the side with the smaller number of molecules

(for gaseous reactions)

If the pressure of a system at equilibrium is decreased, what happens to the equilibrium?

• the equilibrium position will shift towards the side with the larger number of molecules

If the temperature of a system at equilibrium is increased, what happens to the equilibrium?

• equilibrium shifts to the endothermic side to increase products

• the products at the exothermic side decrease

If the temperature of a system at equilibrium is decreased, what happens to the equilibrium?

• equilibrium shifts to the exothermic side to decrease products

• the products at the endothermic side increase

The equilibrium mixture is cooled.

Explain what happens to the concentration of the pink cobalt compound. [3]

• concentration increases

• because equilibrium moves to the left

• because the reverse reaction is exothermic

Suggest why a catalyst is used in this industrial process.

Do not give answers in terms of increasing the rate of reaction. [1]

lowers energy costs

Suggest the effect of using the catalyst on the equilibrium yield of methanol. [1]

catalysts don’t effect the yield

what is meant by a closed system?

a system where the reactants or products cannot escape or enter