Chemical Change & Rate of Reaction (Cambridge (CIE) IGCSE Chemistry)

The line on the graph that represents the reaction that takes place at a higher temperature is A.

The line on the graph that represents the reaction that takes place with a catalyst is A.

The lines on the graph that indicate a reaction that has taken place between acid and

• powdered calcium carbonate: A

• lumps of calcium carbonate: B

Magnesium powder has a greater surface area.

The four factors that can affect the rate of a reaction are:

• The concentration of the reactants in solution or the pressure of reacting gases

• Surface area of solid reactants

• The temperature of the reaction 

• The presence of a catalyst

The graph which will have the steeper gradient is concentrated acid and marble chips.

A steep gradient on a rate of reaction graph indicates a fast rate of reaction.

Increasing the temperature will increase the rate of reaction.

False.

Adding a catalyst to a reaction will increase the rate.

True.

It is of economic interest to have a higher rate of reaction as this implies a higher rate of production and hence a more efficient and sustainable process.

A theory that explains how rates of reaction depend on the frequency and energy of collisions between reactant particles.

False.

Not all collisions result in a chemical reaction. Unsuccessful collisions happen when the colliding species do not have enough energy to break the necessary bonds.

The number of collisions is proportional to the number of particles present.

A successful collision is a collision between reactant particles that leads to the formation of product molecules.

Correct orientation is required for reacting particles to collide effectively and form products.

An unsuccessful collision is one in which the reactant particles just bounce off each other and remain unchanged.

Activation energy is the minimum energy that reacting particles must have for a reaction to occur.

Greater kinetic energy means a greater proportion of collisions will have an energy that exceeds the activation energy. There are more frequent collisions as the particles are moving quicker. Therefore, more collisions will be successful.

Factors affecting the rate of reaction include temperature, concentration, surface area, and the presence of a catalyst.

The minimum energy required for reactant particles to undergo a chemical reaction.

True.

Increasing the concentration of a solution will increase the number of reactant particles in a given volume, allowing more frequent and successful collisions per second.

Increasing temperature increases the kinetic energy of the particles, leading to more frequent and successful collisions with energy greater than the activation energy.

Increasing the surface area of a solid reactant increases the rate of reaction because more surface area is exposed to the other reactant, producing a higher number of collisions per second.

True.

As a rule of thumb for every 10 degree increase in temperature, the rate of reaction approximately doubles

The number of collisions is proportional to the number of particles present.

A catalyst is a substance that increases the rate of a chemical reaction without being consumed in the reaction.

False.

Catalysts are not consumed during the reaction.

The rate of a reaction can be measured by:

• Measuring how quickly the reactants are used up.

• Measuring how quickly the products are formed.

Three techniques used in a lab that are used to measure the rate of a reaction include:

• measuring mass loss on a balance.

• measuring the volume of a gas produced.

• measuring a reaction where there is a colour change at the end of the reaction.

Disadvantages of measuring the rate of a reaction by collecting gas in an inverted measuring cylinder include:

• The delivery tube can pop out.

• It can be hard to read the scale upside down.

• Gas is lost when the bung is connected to the reaction flask.

Disadvantages of measuring the rate of a reaction by collecting gas using a gas syringe include:

• They are fragile and expensive.

• They collect limited volumes.

• Gas can be lost while the bung is connected to the flask.

An advantage of measuring the rate of a reaction via the formation of a precipitate is that no specialist equipment is needed.

Line A shows magnesium powder reacting with acid and line B shows magnesium ribbon reacting with acid.

The reactions takes 30 seconds to complete. The point at which the line plateaus is when the reaction is complete.

Line A is magnesium reacting with concentrated acid, and line B is magnesium reacting with dilute acid.

The reaction is the fastest at the beginning of a reaction. Between 0 and 10 seconds.

True.

The gradient of the line in a rates graph is equal to the initial rate of reaction.

False.

The steeper the gradient of the line in a rates graph then the faster the rate of reaction.

The equation to calculate the gradient is:

Gradient =