Signsofreactions andRates of reactions
What is always formed in a chemical reaction?
Name the type of chemical reaction which releases heat.
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.
Nametwotoxic 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 reactionis not used up by the reactions
How can the course of a reactionbe followed?
By measuring changes in --concentration-mass-volume of reactants and products.
How is the average rate of a reaction calculated?
change in quantitychange in time
In a reaction , 60cm3of gas were collected in 20 s.Calculate theaverage rateof the reaction, in cm3s-1, in the first 20 s.
Change in quantity = 60change in time = 2060/20 = 3.
How is the rate of a reaction calculated?
Rate = 1/time 1/tTime = 1/rate
Whatfactorscan affect therate of a reaction?
ConcentrationTemperatureParticlesizeUseof a catalyst
Howcan the rateof areaction 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