Rate of reactions

Collision theory: for a chemical reaction to happen:

reactant particles must colide with eachother.

the particles must have enough energy for them to react

How can the mean rate of reaction be calculated:

Mean rate of reaction = quantity of reactant used DIVIDED by time taken

Measuring Rate of reaction using a graph gradient:

the steeper the line, the greater the rate of reaction.

The greater the frequency of successful collisions, the greater the rate of reaction. If the concentration of a reacting solution or the pressure of a reacting gas is increased:

• the reactantparticles become more crowded

• the frequency of collisions between reactant particles increases

• the rate of reaction increases

Calculating the rate of reaction from the gradient of a tangent:

rate of reaction = change in mass or volume of product DIVIDED by change in time

If a large lump is divided or ground into a powder:

• its total volume stays the same

• the area of exposed surface increases

• the surface area to volume ratio increases

If the temperature of the reaction mixture is increased:

• reactantparticles move more quickly

• the energy of the particles increases

• the frequency of successful collisions between reactant particles increases

• the proportion of collisions which are successful increases

• the rate of reaction increases

A catalyst is a substance that:

• increases the rate of a reaction

• does not alter the products of the reaction

• is not chemically changed or used up at the end of the reaction

How do catalysts work:

• A catalyst provides an alternative reaction pathway that has a lower activaion energy

Required practicle - Measure the production of a gas ( method )

1. Support a gas syringe with a stand, boss and clamp.

2. Using a measuring cylinder, add 50 cm³ of dilute hydrochloric acid to a conical flask.

3. Add 0.4 g of calcium carbonate to the flask. Immediately connect the gas syringe and start a stop clock.

4. Every 10 seconds, record the volume of gas produced.

5. When the reaction is complete, clean the apparatus as directed by a teacher.

6. Repeat steps 1 to 5 with different concentrations of hydrochloric acid.

Required practicle -investigate the rate of reaction by colour change

1. Using a measuring cylinder, add 50 cm³ of dilute sodium thiosulfate solution to a conical flask.

2. Place the conical flask on a piece of paper with a black cross drawn on it.

3. Using a different measuring cylinder, add 10 cm³ of dilute hydrochloric acid to the conical flask. Immediately swirl the flask to mix its contents, and start a stop clock.

4. Look down through the reaction mixture. When the cross can no longer be seen, record the time on the stop clock.

5. Measure and record the temperature of the reaction mixture, and clean the apparatus as directed by a teacher.

6. Repeat steps 1 to 5 with different starting temperatures of sodium thiosulfate solution.

What is the rate of reaction

The rate of a reaction is a measure of how quickly a reactant is used up, or a product is formed.