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

What is always formed in a chemical reaction? New substance

Name the type of chemical reaction which releases heat. Exothermic

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

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

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

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.

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

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

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

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.

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

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

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