the rate and extent of chemical change Flashcards
(22 cards)
What is the rate of a reaction?
How fast a reaction proceeds
How do you calculate rates of reaction?
-mean rate of reaction = quantity of reactant used ÷ time taken
-mean rate of reaction = quantity product formed ÷ time taken
What are the units for rates of reaction?
g/s or cm3/s
How do you calculate the mean rate of reaction in an experiment where a colour change is timed?
mean rate of reaction = 1 ÷ time taken
Why are catalysts used?
To speed up the rate of chemical reactions
How do catalysts increase the rate of reaction?
They provide an alternate pathway that requires a lower activation energy
What is activation energy?
The minimum energy needed for a chemical reaction to occur
What factors affect activation energy?
-Concentration
-Pressure
-Surface area to volume ratio
How does concentration affect the rate of reaction?
Increasing the concentration of a reactant increases the number of particles present. If more particles are present, then there will be more collisions. If there are more collisions, then the rate of reaction will be greater
How does pressure affect the rate of reaction?
Increasing the pressure increases the number of collisions with the container. The particles themselves will also collide more often. This will lead to a greater rate of reaction
How do you increase pressure?
-Increasing the amount of a gas in a container,
-Decreasing the size of the container
-Heating up the particles
How do you increase surface to volume ratio
Cutting solid reactants into smaller pieces
How does surface area to volume ratio affect the rate of reaction?
Increasing the surface area of solids by cutting solids into
smaller pieces reveals more particles of the solid. This increases the number of particles colliding. The greater the number particles colliding the greater the rate of reaction
How is surface area to volume ratio calculated?
(area of 1 side x number of sides) : (length x width x height)
How does temperature affect rate of reaction?
Increasing the temperature increases the particles kinetic energy. If particles have more energy they move faster. If particles are moving faster, they are more likely to collide and will also collide more energetically. This increases the rate of reaction
How does equilibrium work?
If a reversible reaction takes place in a sealed container it will reach equilibrium when the rate of the forward and reverse reaction is equal
How does changing conditions affect equilibrium?
-Changing the conditions of a reaction that has reached equilibrium will cause the reaction to respond and counteract the change.
-The conditions that can be changed are temperature, pressure, and concentration
How do you show a reaction is reversible?
A + B ⇌ C + D
Which direction will a reaction move if temperature is increased?
endothermic
Which direction will a reaction move if temperature is decreased?
exothermic
How does changing concentration affect equilibrium?
If the concentration of one of the reactants or products is
changed then the reaction will no longer be at equilibrium > if a reaction is no longer at equilibrium the concentrations of all the substances involved in the reaction will change until a new equilibrium is found
How does changing pressure affect equilibrium?
If we increase the pressure in a reaction involving gases the reaction will move to the side with the fewest molecules of gas
