Rates Of Reaction Flashcards
What does the rate of collision depend on?
Collision frequency of reacting particles - more collisions = faster reaction.
Energy transferred during a collision - particles have to collide with enough energy to be successful & break the bonds in the reactants.
What is the activation energy?
The minimum amount of energy required for particles to react.
Particles need this much energy to break the bonds in the reactants & start the reaction.
What happens with a greater activation energy?
Greater activation energy = more energy needed to start the reaction.
What does the rate of reaction depend on?
Temperature.
Concentration/pressure.
Surface area.
Catalyst.
Explain how increasing temperature increases rate of reaction?
Temperature increased = particles move faster = more collisions.
Higher temperature = higher energy of collisions - reactions only happen if particles collide with enough energy.
So higher temperatures = more successful collisions (more particles collide with enough energy to react) per unit time
Explain how increasing concentration (or pressure) increases rate of reaction?
Solution - higher concentration = more particles of reactant in same volume.
More collisions per unit time - rate increases.
Gases - higher pressure = gases more crowded.
Frequency of collisions increase per unit time = higher rate of reaction.
Explain how increasing smaller particles (larger SA) increases rate of reaction?
Higher SA:VOL ratio = particles around the solid will have more area to react = higher frequency of collisions per unit time
What is a catalyst?
Substance that increases rate of reaction without being used up itself.
Explain how catalysts work?
Catalysts decrease the activation energy required for a reaction to occur by providing an alternative reaction pathway with a lower activation energy - speeds up the reaction.
What are the 3 ways that rate of reaction can be measured?
Precipitation.
Change in mass (gas given off).
Volume of gas given off.
Describe the precipitation experiment?
Works for any reaction where mixing 2 see-through solutions produces a cloudy precipitate.
Mix 2 solutions & put in flask above cross.
The faster the cross disappears = faster reaction - disadvantage as subjective over ‘when exactly’.
Describe the change in mass experiment?
Use a mass balance with conical flask + reactants in top.
As gas is released - lost mass measured on balance.
Quicker the reading decreases = faster reaction.
Reaction finished when mass stops changing.
Plot results on graph of change in mass against time.
Safety - e.g. fume cupboard.
Why is cotton wool used at the top of the flask?
Cotton wool lets gases through but stops solid/liquid flying out.
Describe the volume of gas given off experiment?
Gas syringe to measure volume of gas given off.
More gas given off over set time interval = faster rate of reaction.
Reaction finished when no more gas produced.
Plot results on graph of volume given off against time.
Make sure right size of syringe - vigorousness.
Describe an experiment to show how SA affects rate?
Setup apparatus - measured concentration/volume of acid with known mass.
Measure volume of gas given off at regular time intervals with syringe.
Plot graph of volume of gas given off against time.
Repeat experiment with same volume/concentration of acid & same mass of marble chips - but different SA.
