Chemistry 9 Flashcards
Rate and extent of chemical reactions
How do you find the mean rate of reaction?
quantity of reactant used / time taken
or
quantity of product formed / time taken
What is the quantity of reactant/product formed measured in?
Mass: grams
Volume: cm³
moles
What are the units for the rate of reaction?
g/s
or
cm³/s
mol/s
What can affect the rate of chemical reactions?
The concentrations of reactants in the solution The pressure of reacting gases The surface area of solid reactants The temperature The presence of catalysts
What would happen if the concentration of a reacting solution or the pressure of a reacting gas is increased?
The reactant particles become more crowded
The frequency of collisions between reactant particles increases
The rate of reaction increases
What is a reactant?
Substances that are present at the start of a chemical reaction.
What is a catalyst?
A catalyst is a substance that can increase the rate of reaction. Catalysts are not used up during the reaction. They do not alter the products of the reaction. Different reactions need different catalysts.
_______ act as catalysts in biological systems.
Enzymes
Changing the temperature affects…
the frequency of collisions
The energy of collisions
The rate of reaction
Changing the concentration affects…
the frequency of collisions of dissolved reactants
Changing the surface area affects…
the frequency of collisions involving a solid reactant.
A chemical reaction can only take place when…
Reactant particles collide with each other
The particles have enough energy for them to react
What is activation energy?
The minimum amount of energy that colliding particles must have for them to react.
Reactions that occur slowly have…
Reactions that happen quickly have…
a low rate of reaction, e.g. rusting.
a high rate of reaction, e.g. burning and explosions.
What would happen if we increase the temperature (in an experiment)?
The frequency of collisions increases and the collisions become more energetic which increases the rate of reaction.
What would happen if we increase the concentration of reactants in a solution, the pressure of reacting gases or the surface area of solid reactants?
The frequency of collisions increases which increases the rate of reaction.
In some chemical reactions, the products of the reaction can react to produce the original reactants. Such reactions are called reversible reactions.
1) How can we represent these ‘reversible reactions’?
2) How can we change the direction of reversible reactions? Give an example of this.
1) A + B ⇌ C + D
(reactants) (products)
2) By changing the conditions, e.g.
heat
ammonium chloride ⇌ ammonia + hydrogen chloride
cool
If a reversible reaction is __________ in one direction, it is ___________ in the opposite direction. The ____ amount of energy is transferred in each case.
exothermic, endothermic } vice versa, e.g.
endothermic hydrated copper sulphate ⇌ anhydrous copper sulphate + water exothermic
If the concentration of a product is decreased, what will happen?
More reactants will react until equilibrium is reached again.
What is the rate of reaction?
The measure of how quickly a reactant is use up or how quickly a product is formed.