The rate and extent of chemical change. Flashcards
Calculating the rate of reaction equation.
Rate of reaction = amount of reactant used OR product formed/time.
How can the rate of reactants be found?
By measuring the amount of reactants used.
-Measuring the amount of products formed.
-Measuring the time it takes for a reaction mixture to become opaque or change colour.
What are the four factors that affect the rate of reaction?
-Temperature.
-Concentration.
-Surface area.
-Use of a catalyst.
(RP) Investigate how changes in concentration affect the rates of reactions by methods involving the production of gas or a colour change.
1) Set up the equipment shown.
2) Add the hydrochloric acid to the flask and swirl to mix the reactants.
3) Start the timer.
4) Watch the cross through the flask.
5) When the cross is no longer visible stop the timer.
6) Repeat the experiment using hydrochloric acid of a different concentration.
How do you find the rate?
Draw a tangent to the curve at that time.
Find the gradient of the tangent using the equation difference in the amount of product/reactant used time.
The gradient is equal to the rate of reaction at that time.
What is a catalyst?
A catalyst is a substance that increases the rate of a chemical reaction without being used up in the process.
What does a catalyst do?
-Reduces the amount of energy needed for a successful collision.
-Makes more collisions successful.
-Speeds up the reaction.
-Provides a surface for the molecules to attach to which increases their chances of bumping into each other.
What is a reversible reaction?
When the products can react to produce the original reactants.
How are reversible reactions represented?
A(g) + B()g ⇌ C(g) + D(g)
This means that:
-A and B can react to produce C and D.
-C and D can react to produce A and B.
What happens in a closed system?
No reactants are added and no products are removed.
What happens when a reversible reaction occurs in a closed system?
An equilibrium is achieved when the rate of the forward reaction is equal to the rate of the backward reaction.
What does le Chatelier’s principle state?
If a system in equilibrium is subjected to a change in conditions then the system shifts to resist the change.
What happens to reactions involving gases?
-An increase in pressure favours the reaction that produces the least number of gas molecules.
-A decrease in pressure favours the reaction that produces the greater number of gas molecules.
What happens if the concentration of a reactant or product is changed?
-The system is no longer in equilibrium.
-The system adjusts until it can reach equilibrium once more.
If the concentration of one of the reactants is increased, the position of equilibrium shits so that more products are formed until the equilibrium is reached again.
In contrast, if the concentration of one of the reactants is decreased, the position of equilibrium shifts so that more reactants are formed until equilibrium is reached again.
What does a catalyst do to the equiblrium position?
It does not shift the equilibrium position. It only increases the rate of the forward and reverse reaction.
