CHEMISTRY RATES UNIT 3 Controlling the Rate

Controlling the rate

What are the reasons as to why reaction rates must be controlled in industrial processes ?

Reaction rates must be controlled in industrial processes for 2 main reasons : profit (Rate too low won’t make money) and health&safety (rate too high can be dangerous)

What criteria must be met in order for particles to react ?

In order for particles to react, particles must collide with sufficient energy and particles must collide with favourable collision geometry

What is the activation energy ?

Activation energy (Ea) is the minimum energy needed for particles to react together and form an activated complex

How can the activation energy be calculated ?

The activation energy can be calculated by subtracting the potential energy of the reactants from the maximum potential energy in the reaction

What is the activated complex ?

The activated complex is an unstable arrangement of atoms formed when the reactant bonds have broken but the product bonds have not yet formed

When is the activated complex formed ?

The activated complex is formed at the maximum of the potential energy barrier, during a reaction What

What is enthalpy ?

Enthalpy is a measure of the chemical energy in a substance

How to calculate the change in enthalpy (/_\ H) of a reaction

The change in enthalpy for a reaction is the energy difference between the products and the reactants

Name the lines in this FORWARD reaction

What happens during an exothermic reaction and why ?

During an exothermic reaction the energy of the products is less than that of the reactants so energy is released to the surroundings

What happens to the numerical value for enthalpy change in exothermic reactions and why ?

In an exothermic reaction the energy of the products is less than that of the reactants so energy is released to the surroundings, due to this exothermic reactions are given a negative sign before the numerical valve for enthalpy change

What happens during an endothermic reaction and why?

During an exothermic reaction the energy of the products is greater than that of the reactants so energy is absorbed from the surrounding

What happens to the numerical value for the enthalpy change of an endothermic reaction and why ?

In an endothermic reaction the energy of the products is greater than that of the reactants so energy is absorbed from the surroundings, due to this endothermic reactions are given a positive sign before the numerical value for the enthalpy change

How to graph the reverse reaction from the forward reaction ?

To graph the reverse reaction it is the forward reaction flipped around

Name the lines on this REVERSE reaction

What does relative rate measure ?

Relative rate is the measure of the speed at a specific point in the experiment

What does average rate measure ?

Average rate measures the speed of a reaction over a period of time

What is the formula to calculate relative rate ?

How can the relative rate equation be rearranged to calculate the time ?

What apparatus can be used to collect and measure the volume or mass of gas produced in a reaction ?

Gas syringe, measuring cylinder using displacement of water and balance

What effect does concentration have a on the rate of a reaction and why ?

Increasing concentration increases the rate of a reaction

The higher the concentration the more reactant particles there are, this means more collisions. More collisions mean more chance of particles having the activation energy and favourable collision geometry hence the faster rate

How can pressure be increased ?

Pressure can be increased by forcing the existing gas particles into a smaller space and by adding more gas particle into the existing space

What effect does pressure have on rate and why?

Increasing pressure increases the rate of reaction

This is because increasing the pressure in a reaction involving gases reduces the volume for particles to more around in. This results in more collisions, therefore an increased chance of particles having the activation energy and colliding with favourable collision geometry

What effect does surface area/particle size have on rate ?

Increasing the surface area/decreasing the particle size increases the rate of a reaction

The larger surface area the more particles that can collide simultaneously, the more collisions that occur the more chance of collisions occurring between particles with the activation energy and with favourable collision geometry, this leads to an increased rate of reaction

What are 2 factors d which had to be kept constant in the experiments determining the effect of temperature on rate ?

The volume of all the reactants and the concentration of all the reactants had to be kept constant in the experiments determining the effect of temperature on rate

What effect does temperature have on rate and why?

Increasing the temperature increases the kinetic energy of the particles, this means that more particles have the activation energy therefore there are more successful collisions and an increased rate

State the colour change observed in the reaction used to determine the effect of temperature on rate

In the reaction to determine the effect of temperature on rate there is a colour change observed from purple to colourless

What is temperature a measure of ?

Temperature is a measure of the average kinetic energy of the particles in a substance

What does the arrow represent ?

An increased temperature meaning that more particles have activation energy

What does the total area under a kinetic energy distribution diagram curve show ?

The total area under a kinetic energy distribution diagram curve shows the energy distribution of all reactants

What will happen to the curve in a kinetic energy distribution diagram if the temperature is increased

If the temperature is increased the peak of the curve will lower and move to the right

What happens to the activation energy when the temperature is increased ?

The activation energy does not change when temperature is altered

What is a catalyst ?

A catalyst is a substance which speeds up a reaction but is not consumed in the reaction

What effect do catalysts have on the activation energy and what does this allow for ?

Catalysts lower the activation energy which makes it easier for an activated complex to form

How do catalysts reduce the activation energy ?

Catalysts reduce the activation energy of a reaction by providing an alternative route for the reaction to proceed

What is A and B

A- uncatalysed reaction

B- catalysed reaction

What happens to the line representing the activation energy in a kinetic energy diagram when a catalyst is used ?

When a catalyst is used the activation energy decreases and so the line representing the activation energy moves to the left

How does a catalyst speed up a reaction ?

The use of a catalyst will cause more particles to have energy greater than the activation energy to react and so the rate of reaction will increase