Rates of reactions

1. Rates of reactions State how the rates of chemical reactions of kitchen chemicals are effected by; concentration, particle size, temperature, mixing, catalysts

2. Reactions: • For a reaction to occur there must be at least 2 chemicals present. • The chemicals need to come in contact with one another and have enough energy to react. • The reaction rate is how fast a reaction happens. Reactions can be sped up or slowed down. A + B -> C + D • In a reaction the starting chemicals are called reactants (A & B) • The new chemicals are called products (C & D) • We can measure how quickly a substance is used up (e.g. marble chip dissolves) • Or how quickly new substances are formed (e.g. gas) 

3. concentration • The higher the concentration, the faster the reaction goes. • Concentration: how strong a chemical is. • The more concentrated a chemical is the more particles it has. • With more particles in the same space there is an increase in the number of collisions.

4. Mini Experiment • Aim: to compare the rate of reaction between 2 different concentrations of acid and Mg metal • Method: Collect: 2 molL-1 acid and 0.5 molL-1 acid, 2 test tubes, 2 pieces of Mg metal, 10mL measuring cylinder, glasses • accurately measure 3mL 0.5 molL-1 acid, and place in one test tube • accurately measure 3mL 2 molL-1 acid, and place in another test tube • Place 1 piece of Mg metal into the first test tube and time how long it takes until the reaction stops. • Repeat using the 2nd test tube (2 molar).

5. Results: • 0.5 molL-1 acid time: _______________ • 2 molL-1 acid time: ________________ • Fastest one was the ___________ • Conclusions: • The ___________ acid was fastest because it is __________ concentrated. It had a lot _________ acid particles in it. • Equation: copy from the whiteboard

6. Particle size: • The collisions in a reaction only occur on the exposed surface area of a solid. • The more particles that are exposed, the more collisions that can occur.

7. Mini experiment: • Aim: to compare the reaction between a small surface area and large surface area • Method: • Collect: 2 test tubes, safety glasses, 2 molL-1 acid, 1 large marble chip, equivalent amount of powdered marble chip, 2 10 mL measuring cylinders. • Add the large marble chip to one test tube and the powdered to the other. • Accurately measure 3mL of acid and place into each test tube at the same time. • Record what happens? Write down all you see and hear, compare the 2 test tubes.

8. Results: • Chip: ___________________________________________ ________________________________________________ • Powdered: _______________________________________ ________________________________________________ • The difference: ___________________________________ ________________________________________________ • Conclusion: • The ______________ was more ….. • Equation: copy from the whiteboard

9. Rates of reaction: temperature • When the temperature is increased, the particles move faster. • Because they move faster, there is an increased chance of collisions. • Because they have more energy, the collisions have more energy also and so they are more likely to react.

10. Rates of reaction: Mixing • When you mix something, the particles are moved around one another and so there is an increased chance of reacting. • E.g. sugar in a cup of coffee, without mixing (stirring) the sugar will dissolve eventually, but with mixing it only takes a couple of seconds to dissolve

11. Rates of reaction: Catalyst: • A catalyst speeds up a reaction but doesn’t take part in the reaction. • It works by lowering the amount of energy needed for a reaction to occur. • This means that the particles don’t have to collide with the same amount of energy as with no catalyst.