Rates of reaction Flashcards
What effect does increasing temperature have on the rate of reaction?
Increasing temperature in a reaction gives the particles greater kinetic energy, so they move a lot faster. More particles have energy greater than the activation energy, increasing the number of successful collisions per unit time.
What effect does increasing the concentration have on the rate of reaction?
Increasing the concentration of a solution or pressure of a gas increases the number of particles in the same volume, increasing the number of collisions per unit time and therefore increasing the chance of successful collisions.
What effect does increasing the surface area have on the rate of reaction?
Increasing the surface area increases the number of particles available to collide, increasing the number of collisions per unit time and increasing the chance of successful collisions occurring.
What effect does adding a catalyst have on the rate of reaction?
Adding a catalyst provides an alternate reaction pathway with less energy required to break the bonds (lower activation energy). A greater number of particles will possess the activation energy, increasing the chance of successful collisions occurring.
What is a homogenous catalyst?
A catalyst that is in the same phase as the reactants, they take an active part in the reaction and are regenerated as the reaction proceeds.
What is a heterogenous catalyst?
A catalyst that is in a different phase from the reactants. They provide a surface for the reactant particles to absorb and desorb to.
What is the activation energy?
The minimum energy required to start a reaction by breaking bonds.
What is the rate of reaction?
The change in concentration of a reactant or product per unit time.
What also effects the rate of reaction?
Light.
How do you study change in gas volume in a reaction?
The volume of gas can be recorded by using a gas syringe at various times.
How do you study change in gas pressure in a reaction?
This involves a change in the number of moles of gas. The change in pressure can be followed using a monometer.
How do you study change in mass in a reaction?
If gas forms in a reaction and is allowed to escape, the change in mass can be followed using a weighing balance.
How do you study change in colour in a reaction?
The concentration of the substance changing colour can be measured using a colorimeter.
Describe a method of gas collection
- Start the reaction by shaking the metal into the acid and start a stopwatch
- Measure the amount of hydrogen given off at constant intervals and stop the watch when it is no longer produced
- Repeat the experiment with different concentrations or temperature of the acid and particle size of the metal
- Draw a graph of your results
How does an iodine-clock reaction work?
Iodide ions can be oxidised to iodine at a measurable rate. Iodine gives a strongly coloured blue complex with starch solution but with a given amount of thiosulphate ion added, no blue will appear until enough iodine has formed to react with the thiosulphate ions.
Why must temperatures be kept constant in iodine-clock and precipitation reactions?
Since rates vary rapidly with changes in temperature.
Describe how to carry out an iodine-clock reaction
- Measure known volumes of acid, thiosulphate solution and iodide solution in a conical flask and add starch
- Measure a known volume of hydrogen peroxide into a test tube
- Rapidly pour the peroxide into the flask, start a stopwatch and mix thoroughly
- When the colour disappears, stop the watch
- Repeat using five concentrations of peroxide, ensuring the volume is constant
- Plot a graph of 1/time against volume of peroxide
Describe how to carry out a precipitation reaction experiment
- Measure a known volume of thiosulphate solution into a conical flask
- Measure nitric acid into a test tube
- Rapidly pour the acid into the flask, start a stopwatch and mix thoroughly
- Place the flask over a black cross and stop the watch when the cross can no longer be seen
Give an example of a homogenous catalyst
Concentrated sulphuric acid the the formation of esters from carboxylic acids and alcohols.
Give an example of a heterogenous catalyst
Iron in the Haber process for ammonia production.
