3.9-3.16 Rates of reaction

Reactions take place at different rates depending on…

1. Chemicals involved

2. Conditions of reaction

What is an example of a slow reaction?

Rusting

What is an example of a fast reaction?

Explosions

Fill in the gaps for investigating the effect of SA on rate of reaction:

1. Add dilute [ ] to the conical flask

2. Use a [ ] [ ] to connect this flask to an [ ] [ ] [ ] [ ] [ ] in a [ ] [ ]

3. Add [ ] [ ] [ ] into the [ ] [ ] and close the bung

4. Measure the [ ] of gas produced in a [ ] time using the measuring cylinder

5. Repeat with different [ ] of [ ] [ ] [ ]

1. Add dilute HCl to the conical flask

2. Use a delivery tube to connect this flask to an inverted measuring cylinder upside down in a water trough

3. Add calcium carbonate chips into the conical flask and close the bung

4. Measure the volume of gas produced in a fixed time using the measuring cylinder

5. Repeat with different sizes of calcium carbonate chips

Fill in the gaps for investigating the concentration of a solution on rate of reaction:

1. Measure 50 cm³ of [ ] [ ] solution into a flask

2. Measure 5 cm³ of dilute [ ] into a measuring cylinder

3. Draw a [ ] on a piece of paper and put it [ ] the flask

4. Add the acid into the flask and [ ] [ ] [ ] [ ]

5. Look down at the [ ] [ ] [ ] and stop the stopwatch when the cross [ ] [ ] [ ] [ ] [ ]

6. Repeat using [ ] [ ] of sodium [ ] solution (mix different volumes of sodium thiosulfate solution with water to dilute it)

1. Measure 50 cm³ of sodium thiosulfate solution into a flask

2. Measure 5 cm³ of dilute HCl into a measuring cylinder

3. Draw a cross on a piece of paper and put it underneath the flask

4. Add the acid into the flask and immediately start the stopwatch

5. Look down at the cross from above and stop the stopwatch when the cross can no longer be seen

6. Repeat using different concentrations of sodium thiosulfate solution (mix different volumes of sodium thiosulfate solution with water to dilute it)

What will happen to the rate of reaction due to the concentration of a solution increasing?

The rate of reaction will increase

Why does increased concentration increase rate of reaction?

More reactant particles in a given volume, allowing more frequent collisions

The number of collisions is [ ] to the number of particles present

Proportional

Fill in the gaps for investigating the effect of temperature on rate of reaction:

1. Dilute HCl is heated to a [ ] [ ] [ ] [ ] [ ]

2. Add the dilute HCl into a [ ] [ ]

3. Add a [ ] [ ] [ ] and [ ] [ ] [ ]

4. Stop the time when the magnesium [ ] [ ]

5. Repeat at different temperatures and compare results

1. Dilute HCl is heated to a set temperature using a water bath

2. Add the dilute HCl into a conical flask

3. Add a strip of magnesium and start the stopwatch

4. Stop the time when the magnesium fully dissolves

5. Repeat at different temperatures and compare results

Why does increasing temperature increase rate of reaction?

Particles have more kinetic energy than the required activation energy, so more frequent and more energetic collisions will occur

What are factors that can affect the rate of a reaction?

• The [ ] of the reactants in solution or the [ ] of reacting gases

• The [ ] of the reaction 

• [ ] [ ] of solid reactants

• The presence of a [ ]

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

• The temperature of the reaction 

• Surface area of solid reactants

• The presence of a catalyst

Why is it of economic interest to have a higher rate of reaction?

Implies a higher rate of production and hence a more efficient and sustainable process

Increasing the pressure means that there are the same number of reactant particles in a [ ] volume

Smaller

What are catalysts?

Substances which speed up the rate of a reaction without themselves being altered or consumed in the reaction

What are widely regarded as catalysts as they have variable oxidation states to readily donate and accept electrons?

Transition metals

What represents the overall enthalpy change of a reaction in reaction profiles?

The difference in height between the energy of the reactants and of the products

What does the initial increase in energy represent?

The activation energy required to start the reaction

What do catalysts do to the activation energy?

Catalysts lower the activation energy

Why does lowering activation energy increase rate of the catalysed reaction?

A greater proportion of the molecules in the reaction mixture will have sufficient energy for an effective collision

Why do reactions with a low activation energy occur readily?

Little energy is needed to break the bonds to start the reaction