C6 Rates

What is rate of reaction?

a measure of how quickly reactants form products

What equations are used to calculate the mean rate of reaction? (2)

quantity of reactant used / time
quantity of product formed / time

What are the units of rate of reaction? (2)

g/s

cm³/s

What are the usual units for mass (in chemistry)?

g

What are the units for volume

cm³

A steep gradient on a rate of reaction graph shows what?

fast reaction

What does it mean when a graph showing rate of reaction levels off?

the reaction is complete and no more product is produced

What is concentration?

The number of particles in a given volume

What is pressure?

A measure of how close together gas particles are

What is surface area?

The area of a solid that is exposed to the surface

How could you increase the surface area of a solid reactant?

Break it into smaller pieces

Which has a larger surface area: 10 g of magnesium ribbon or 10 g of magensium powder?

10g of magnesium powder

What happens to the rate of a reaction when the concentration of reactants in solution is increased?

rate increases

What happens to the rate of a reaction when the pressure of reacting gases is increased?

rate increases

What happens to the rate of a reaction when the temperature is increased?

rate increases

What happens to the rate of a reaction when the surface area of solid reactants increases?

rate increases

What happens to the rate of a reacton when a solid reactant is broken into smaller pieces?

rate increases

What methods can you use to collect a gas? (2)

a gas syringe

in an upturned measuring cylinder underwater

What piece of apparatus should be used to measure 20 cm³ of acid?

a measuring cylinder

When will solutions turn cloudy?

When an insoluble solid is produced

Why can measuring the time taken for a solution to turn cloudy indicate the rate of reaction? (2)

The solution turns cloudy when the product is formed

Measuring the time allows us to use quantity of product formed / time

What is collision theory?

for chemical reactions to occur, reacting particles must collide with sufficient energy

What is the activation energy?

the minimum amount of energy that reacting particles must collide with for a reaction to occur

What happens if reacting particles collide with energy less than the activation energy?

no reaction - they stay as reactants

What happens if reacting particles collide with energy greater than or equal to the activation energy?

the reaction takes place - the reactants form products

What does the term 𝒇𝒓𝒆𝒒𝒖𝒆𝒏𝒄𝒚 𝒐𝒇 𝒄𝒐𝒍𝒍𝒊𝒔𝒊𝒐𝒏𝒔 mean?

the number of collisions that occur in a given time period eg. collsions per second

How can you increase the rate of a reaction? (2)

Increase the frequency of collisions

Increase the energy of collisions

Why does increasing the surface area increase the rate of a reaction? (3)

increases the number of particles available for collisions

increases the frequency of collisions

increases the chances of successful collisions with energy greater than the activation energy

Why does increasing the concentration of reactants increase the rate of a reaction? (3)

increases the number of particles in a given volume

increases the frequency of collisions

increases the chances of successful collisions with energy greater than the activation energy

Why does increasing the pressure of reacting gases increase the rate of a reaction? (3)

causes the particles to become closer together

increases the frequency of collisions

increases the chances of successful collisions with energy greater than the activation energy

Why does increasing the temperature increase the rate of a reaction? (3)

increases the kinetic energy of particles

increases the frequency and energy of collisions

increases the chances of successful collisions with energy greater than the activation energy

What are catalysts?

Substances that increase the rate of chemical reactions without getting used up themselves

Why does using a catalyst increase the rate of a reaction? (2)

they offer a different reaction pathway with a lower activation energy

this increases the chances of succesful collisions with energy greater than the activation energy

What does a reaction profile for a catalysed reaction look like?

a profile with a lower energy reaction pathway for the reaction with a catalyst

What does this symbol ⇌ mean?

a reversible reaction

What is a reversible reaction?

A reaction in which reactants form products and the products can react to form the reactants

How can the direction of a reversible reaction be changed?

by changing the conditions (e.g. heat for one direction, cool for the other direction)

What is an exothermic reaction?

A reaction that transfers energy to the surroundings

What is an endothermic reaction?

A reaction that takes in energy from the surroundings

If a reversible reaction is exothermic in one direction, what type of reaction is the reverse reaction?

Endothermic