1. Signs of reactions and Rates of reactions
NAT 5 1 2 3 4 5 6 7 8 9 10 11 12 13

2. What is always formed in a chemical reaction?
New substance

3. Name the type of chemical reaction which releases heat.
Exothermic

4. What changes indicate a chemical reaction has taken place?
Colour change, energy change, gas given off, effervescence, precipitation

5. What is an enzyme? A biological catalyst.
They catalyse reactions which take place in the living cells of plants and animals.

6. Why are cars fitted with catalytic converters ?
The convert harmful gases into less harmful gases.

7. Carbon monoxide is converted to carbon dioxide.
Name two toxic gases produced in a car engine. What does a catalytic converter change them to?
Carbon monoxide is converted to carbon dioxide.
Oxides of nitrogen are converted to nitrogen.

8. What is a catalyst?
A substance which -
speeds up a chemical reaction
is not used up by the reactions

9. How can the course of a reaction be followed?
By measuring changes in -
-concentration
-mass
-volume of reactants and products.

10. How is the average rate of a reaction calculated?
change in quantity
change in time

11. Change in quantity = 60 change in time = 20 60/20 = 3.
In a reaction , 60cm3 of gas were collected in 20 s. Calculate the average rate of the reaction, in cm3 s-1, in the first 20 s.
Change in quantity = 60
change in time = 20
60/20 = 3.

12. How is the rate of a reaction calculated?
Rate = 1/time 1/t
Time = 1/rate

13. What factors can affect the rate of a reaction?
Concentration
Temperature
Particle size
Use of a catalyst

14. How can the rate of a reaction be increased?
Increase concentration - increase rate Increase temperature - increase rate ( except when using an enzyme ) Decrease particle size - increase rate Use of catalyst - increase rate