C8- Rates of Reaction Flashcards
. How can you work out the rate of a chemical reaction? (2)
The rate of a chemical reaction can be found by measuring the quantity of a reactant used or the quantity of product formed over time: mean rate of reaction = quantity of reactant used / time taken mean rate of reaction = quantity of product formed / time taken
- How can the quantity of reactant or product be measure? (2)
The quantity of reactant or product can be measured by the mass in grams, by a volume in cm3.
- What are the units for rate of reaction? (2)
The units of rate of reaction may be given as g/s or cm3/s.
- When will a chemical reaction occur? (2 marks)
When reacting particles collide with each other AND with sufficient energy
- How can a graph of time vs amount of product produced be used to compare rates of reaction? (2 marks)
The steeper the gradient, the faster the reaction.
- What does it mean when the graph levels off and goes flat? (1 mark)
It means the reaction is complete and no more product is being produced
- Why do the lines curve before levelling off/going flat? (2 marks)
As the reaction proceeds the concentration of reactants decreases, decreasing the rate of reaction, so the gradient decreases. As the reaction proceeds, the concentration of product increases, which further decreases the concentration of reactants, decreasing the rate of reaction, so the gradient decreases.
- Name 2 factors which affect the rates of chemical reactions? (2)
Factors which affect the rates of chemical reactions include the surface area of solid reactants.
- How does changing the surface area of chemical reactants affect the rate of chemical reactions? (1)
Increasing the surface area leads to an increase in the rate of chemical reactions.
- Describe collision theory. (3)
Collision theory explains how various factors affect rates of reactions. According to this theory, chemical reactions can occur only when reacting particles collide with each other and with sufficient energy. The minimum amount of energy that particles must have to react is called the activation energy.
- How does increasing the surface area of solid reactants affect the frequency of collisions?
Increasing the surface area of solid reactants increases the frequency of collisions and so increases the rate of reaction.
- What is the name of the minimum amount of energy that particles need to react? (1 mark)
Activation energy
- How does increasing the surface area of solid reactants affect the rate of reaction? (2 marks)
Increasing the surface area increases the frequency of collision and increases the rate of reaction.
- How does increasing the temperature affect the rate of reaction? (2 marks)
Increasing the temperature increases the speed of the reacting particles. This makes them collide more frequently and the rate of reaction increases.
- How does increasing the pressure of reacting gasses affect the rate of reaction? (2 marks)
Increasing the pressure increases the frequency of collisions and increases the rate of reaction.
- How does increasing the concentration of reactants affect the rate of reaction? (2 marks)
Increasing the concentration increases the frequency of collisions and increases the rate of reaction.
- How does increasing the surface area of solid reactants affect the rate of reaction? (2 marks)
Increasing the surface area increases the frequency of collision and increases the rate of reaction.
- What is a catalyst? (2 marks)
Catalysts change the rate of chemical reactions but do not get used up during the reaction.
- In what situations can catalysts be useful? (2 marks)
Catalysts are often used in industrial processes to reduce costs. They do this by a) speeding up the reaction so the product is produced more quickly b) allowing the reaction to be carried out at a lower temperature
- What happens with energy when a chemical reaction occurs? (2 marks)
Energy is either transferred to or from the surroundings
- What is a reversible reaction?
In a reversible reaction, the products can react to produce the original reactants again
- What is an exothermic reaction? (1 mark)
A reaction that gives out energy to the surroundings (these reactions can feel hot)
- Give some examples of exothermic reactions (3)
Combustion Many oxidation reactions Neutralisation
- What are some everyday uses of exothermic reactions?(2)
Self-heating cans (e.g for coffee). Hand warmers.
- What is an endothermic reaction?(1)
A reaction that takes in energy from the surroundings (these reactions can feel cold)
- Give some examples of endothermic reactions(1)
Thermal decomposition
- What are everyday uses of endothermic reactions?(1)
Sports injury packs
- If a reaction is reversible and is exothermic in one direction, what will it be in the opposite direction? (1 mark)
Endothermic
Exothermic
hydrated copper sulfate (blue) –><– anhydrous copper sulfate (white) + Water
Endothermic
- If a reaction is reversible and is endothermic in one direction, what will it be in the opposite direction? (1 mark)
Exothermic
Exothermic
hydrated copper sulfate (blue) –><– anhydrous copper sulfate (white) + Water
Endothermic
- What can be said about the energy given out and the energy taken in a reversible reaction? (1 mark)
They are the same (If a reaction gives out 100J in one direction then it will take in 100J in the other)
- Define a dynamic equilibrium (1)
A state of balance between continuing processes.
- Describe a closed system (1)
A system in which there is an exchange of energy (as heat or work) but not matter, with its surroundings.
