Which way energy is transferred in each type of reaction, everyday examples and uses, and the required practical measuring temperature change.
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1.What is an exothermic reaction?
A reaction that transfers energy to the surroundings, so the temperature of the surroundings increases.
2.What is an endothermic reaction?
A reaction that takes in energy from the surroundings, so the temperature of the surroundings decreases.
3.Is energy conserved in a chemical reaction?
Yes. Energy is never created or destroyed, only transferred between the reacting substances and their surroundings.
4.Give four examples of exothermic reactions.
Combustion, oxidation reactions such as rusting, neutralisation, and most displacement reactions.
5.Give two examples of endothermic reactions.
Thermal decomposition, and the reaction between citric acid and sodium hydrogen carbonate.
6.Give an everyday use of an exothermic reaction.
Self heating cans and hand warmers.
7.Give an everyday use of an endothermic reaction.
Instant cold packs used to treat sports injuries.
8.Why does the temperature of the surroundings rise in an exothermic reaction?
Energy is released from the reaction into the surroundings, which is detected as a temperature increase.
9.Is combustion exothermic or endothermic?
Exothermic. It releases a large amount of energy as heat and light.
10.Is thermal decomposition exothermic or endothermic?
Endothermic. Energy must be supplied continuously to break the compound down.
11.In the required practical, what is being investigated?
How a variable such as concentration or the mass of a reactant affects the temperature change of a reaction.
12.Why is a polystyrene cup used rather than a glass beaker?
Polystyrene is a good insulator, so it reduces energy transfer to the surroundings and gives a more accurate temperature change.
13.Why is a lid used on the cup?
To reduce energy lost by evaporation and to the air above the mixture.
14.How is the temperature change calculated?
Final temperature minus starting temperature.
15.What does a negative temperature change indicate?
The reaction is endothermic, because the mixture got colder.
16.Name two variables that must be controlled in this practical.
The total volume of solution, the starting temperature, and the same type and size of container each time.
17.Why is the reaction stirred?
To make sure the mixture and the temperature are even throughout, so the thermometer reading is representative.
18.Give one source of error in this practical.
Energy is still lost to the surroundings despite insulation, so the measured temperature change is smaller than the true value.
19.How could the accuracy of the temperature reading be improved?
By using a digital thermometer or a data logger, which can be read more precisely than a glass thermometer.
20.Is neutralisation exothermic or endothermic?
Exothermic. The temperature rises when an acid and an alkali react.
21.Why do hand warmers eventually stop working?
The reactants are used up, so no more energy can be released.
22.If a reaction mixture feels cold, what type of reaction is it?
Endothermic. It has taken energy from the surroundings, including from your hand.
23.Does an exothermic reaction lose energy overall?
Not overall in the universe. Energy is transferred from the chemicals to the surroundings, so the total is unchanged.
24.Why must temperature be measured immediately after mixing?
Energy is lost to the surroundings over time, so waiting would give a lower peak temperature.
25.What would you plot to show the effect of concentration on temperature change?
Concentration on the x axis and temperature change on the y axis.
26.Why does adding more of a reactant eventually stop increasing the temperature rise?
The other reactant becomes limiting, so no further reaction can occur no matter how much is added.
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