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How would you calculate the mean rate of reaction?
Quantity of product formed or reactant used up/time
Which factors affect the rate of chemical change? And how?
Concentration (more reactant particles means more collisions)
Pressure (more particles within given volume, increased number of collisions)
Temperature (increased energy particles collide with and increased speed means more collisions)
Surface area (more surface particles can collide over)
Presence of catalyst (lowers activation energy, provides alternative reaction pathway)
Required practical for rate of reaction: Turbidity/colour change
Add 10cm³ of sodium thiosulfate solution, ensure concentration is known, to a conical flask atop a black cross
Add 10cm³ of hydrochloric acid
Swirl flask gently and start stopwatch. Stop the watch after cross can no longer be seen.
Repeat process with different concentrations of sodium thiosulfate solution
Define collision and activation theory
Collision theory - Chemical reactions can occur only when reacting particles collide with each other and with sufficient energy.
Activation energy - The minimum amount of energy required for reaction to take place
Define equilibrium and Le Chatelier’s Principle
Equilibrium - When the forward and backward reaction occur at the exact same rate
Le Chatelier’s Principle - When a change is made to a system at equilibrium, the system moves to counteract that change
What happens if you change the concentration (providing the system is at equilibrium)?
If the concentration of reactants is increased, more products will be formed
If the concentration of products is decreased, more reactants will react
What happens if you change the temperature (providing the system is at equilibrium)?
An increase in temperature means the endothermic reaction will be favoured.
A decrease in temperature means the exothermic reaction will be favoured.
What happens if you change pressure (providing the system is at equilibrium)?
An increase in pressure favours the side with the least amount of moles
A decrease in pressure favours the side with the most amount of moles
