Rate Of Reactions Flashcards
How do you work out the mean rate of reaction?
mean rate of reaction = quantity of reactant used or product formed / time taken
Which factors affect the rates of chemical reactions?
- concentration of solution
- pressure of reacting gases
- surface area of solid reactants
- the temp
- use of catalysts
What does the collision theory state?
The more collisions there are the faster the reaction is.
What is the purpose of a catalyst?
A catalyst is a substance that speeds up a reaction without being used up in the reaction. It provides an alternative route for reaction and lowers activation energy.
IS NOT USED UP IN THE REACTION
What is a reversible reaction?
Where the products in a reaction can react to produce original reactants.
What does it mean if a reversible reaction is exothermic?
If it is exothermic in one direction, it will be endothermic in the opposite direction as the same amount of energy is being transferred.
What Is meant by ‘equilibrium’ ?
Equilibrium is reached when the forward and reverse reactions occur at the same rate
What happens if conditions are changed at equilibrium?
If a SYSTEM is at equilibrium and a change is made to the conditions, the system responds to counteract the change.
What is Le Chatelier’s Principle?
The idea that if you change the conditions of a reversible reaction at equilibrium, the system will try to counteract the change.
Used to predict the effect of changes made to a reaction system.
What happens if the temperature is changed at equilibrium?
Increased- amount of products at equilibrium increases for an endothermic reaction.
Decreased- amount of products at equilibrium decreased for an endothermic and increases for an exothermic reaction.
What happens if the pressure is changed at equilibrium?
Increased- equilibrium position shifts to the side with the fewer molecules.
Decreased- equilibrium position shifts to the side with the most molecules (change counteracted)
What is an endothermic reaction?
Takes in energy from the surroundings. Shown by a fall in temperature.
What is an exothermic reaction?
Where energy is transferred to the surroundings, usually by heating. This is shown by a rise in temperature.
E.g combustion reactions
How can we measure the rate of reaction in an experiment?
- collecting gas and reading volume from gas syringe
- see if a precipitate has been formed/colour change
- fizzing/effervescence (observations)
- measure starting mass of reactants and mass of products after reaction and time it
What is the tangent on the graph?
Draw a tangent on the graph and use it to calculate the gradient of the line.
Change in y / change in x
