Rates of Reaction Flashcards
When do reactions take place?
When particles collide with a certain amount of energy (activation energy)
What is the activation energy?
The minimum amount of energy needed for the particles to react. It is different for each reaction.
If particles do not have this amount of energy, the collisions are unsuccessful and do not need to a chemical reaction.
What is the rate of a reaction?
The speed of a reaction.
How can the rate of a reaction be altered?
The rate of a chemical reaction can be altered by changing how often the particles collide and with how much energy (the frequency of collisions between particles and the energy with which particles collide).
1.change the temperature of the reaction
2. change the concentration of solutions
3. change to the surface area of a solid reactant
4. add a catalyst
what happens if particles collide with less energy than the activation energy?
They will not react and the particles will just bounce off each other.
What does increasing the temperature do to the reaction?
It gives all particles more kinetic energy and they move around more quickly. The higher the temperature, the faster the rate of a reaction.
Particles collide with enough kinetic energy to overcome the activation energy and so there are more frequent successful collisions.
Why does increasing the concentration increase the rate of reaction?
As concentration increases, there are more particles in a given volume. This means there are more frequent successful collisions.
At high concentration, the rate is fast. At low concentration, the rate is slow.
How do you increase the surface area of a solid?
To increase the surface area of a solid, you can split it into several pieces. Larger pieces have lower surface area than smaller pieces.
Why does increasing the surface area of a solid reactant increase the rate of reaction?
The smaller the pieces, the larger the surface area (to volume ratio).
This means there are more opportunities for collisions to occur and since the same proportion of collisions will have greater than the activation energy, this also means there will be more frequent successful collisions.
What are catalysts?
Substances that increase the rate of a reaction without being used up in the reaction.
Only a small amount of a catalyst is needed and different reactions require different catalysts.
What do catalysts do?
They speed up the rate of a chemical reaction and give the reaction an alternative pathway that has a lower activation energy.
The activation energy for the reaction is lowered and so more particles can react on collision and so the rate of the reaction is faster.
What is the initial rate of a reaction?
The rate at the start of the reaction. The reactants are at their highest concentration.
Collisions between reacting particles are at a maximum, and therefore more successful collisions are possible leading to the fastest rate, shown on a graph as the steepest part of the curve.
The reaction between calcium carbonate and hydrochloric acid
The reaction between calcium carbonate and hydrochloric acid is followed by measuring the rate of which carbon dioxide is evolved.
The same reaction could also be shown on a graph by following the decreasing concentration of the acid, or the loss of mass of the carbon dioxide escape.
What is the reactant that runs out called?
It is the ‘limiting factor’ for the reaction.
What is the reaction between sodium thiosulphate and hydrochloric acid?
The reaction between sodium thiosulphate and hydrochloric acid produces sulphur.
sodium thiosulphate + hydrochloric acid —> sodium chloride + sulfur + water
Why does the solution turn cloudy in the conical flask experiment?
The sulphur is solid so it turns the solution cloudy.
What does the reaction between sodium thiosulphate and hydrochloric acid investigate?
This experiment investigates the effect of changing the temperature of the sodium thiosulphate on the rate of reaction.
As the temperature of the sodium thiosulphate increases, so does the rate of reaction.
What five things do you have to remember when plotting a graph?
Remember to:
—> Label axes
—> Plot points accurately
—> Draw line/curve of best fit, looking for obvious anomalous results
—> Make the scale linear, starting axes at 0
—> Give the graph a title, if required
