What is the rate of reaction and how can you find it out?
To find the rate of reaction, find out how fast the reactants are used up as they make products or how fast the products are made. Collect this data by:
- Measure the rate at which the reaction mixture mass changes, if the reaction emits a gas. The mass will decrease. Measure and record the mass at regular time intervals. You can attach the balances to a data-logger to monitor the loss of mass continuously. Wear goggles.
- Measure the increasing gas volume emitted if the reaction emits a gas. Collect the gas and measure the volume emitted at time intervals. Wear goggles.
- Measure the decreasing light passing through a solution if the reactants in solution make a suspension of a precipitate (insoluble solid), making the solution go cloudy. Wear goggles.
To find the reaction rate at a given time
- Draw a tangent at the time and form a right angle triangle
- Using the tangent as the hypotenuse
- Calculate the rate.
mean reaction rate = quantity (of reactant/product) formed/time
When do reactions occur?
- Reactions occur when reactant particles come together, and they need to collide with enough energy to cause a reaction (collision theory).
- Activation energy is the minimum energy particles must have before they react.
- Reactions are more likely to occur if there is an increase in their internal energy (the energy they have) or the frequency of collisions.
What is the effect of surface area/SA:V on rate of reaction?
- Smaller pieces increase the surface area so more is exposed to react, increasing reaction rate.
- Particles in a large lump aren't in contact with the solution's reactant particles so can't react until the surface particles have reacted.
- Smaller pieces also mean a larger surface area to volume ratio (SA:V).
- As the side of a cube decreases by a factor of 10, its SA:V increases by a factor of 10.
- A larger surface area of reactant particles is exposed for the same volume, so a larger SA:V means a faster reaction.
What is the effect of temperature on rate of reaction?
- When temperature increases, so does reaction rate, because particles collide more often and with more energy.
- Lowering temperature slows down the reaction rate. Particles colliding more often increases the chances of a reaction.
- An increased proportion of particles exceeding the activation energy has a greater effect on rate of reaction than increased collision frequency.
- As temperature increases, time taken to finish reacting decreases.
The effect of pressure/concentration
- Increasing the concentration of reactants in a solution increases reaction rate since there are more reactant particles moving around in the same volume of solution, meaning there is an increased collision frequency.
- Increasing gas pressure squashes the gas particles more closely together so there're more in a given space, increasing collision frequency.
- Investigate the effect of changing concentration by reacting marble chips with different concentrations of hydrochloric acid.
- Find the reaction rate by plotting the volume of carbon dioxide emitted as the reaction progresses, or measure gas volume at regular intervals, or time how long it takes to collect a fixed gas volume.
CaCO3 (s) + 2HCl (aq) = CaCl (aq) + CO2 (aq) + H2O (l)
Or vary sodium thiosulfate's concentration, and increase the reaction mixture's turbidity as the reaction progresses. Wear goggles.
NaSO2O3 (aq) + 2HCl (aq) = 2NaCl (aq) + H2O (l) + SO2 (aq) + S (s)
Written by Bryant Wong (Chemistry)
- educationquizzes.com, https://www.educationquizzes.com/gcse/chemistry/rates-of-reaction-1/
- clutchprep.com, https://www.clutchprep.com/chemistry/practice-problems/104297/the-activation-energy-for-some-reaction-x2-g-y2-g-2xy-g-is-167-kj-mol-and-e-for-