UNIT 3 – CHEMICAL WORLD


Summary questions 1. Describe the difference between an endothermic reaction and an exothermic reaction.


2. Give an everyday example of: a. an endothermic reaction b. an exothermic reaction


3. The table below shows the temperature changes that take place when substances are dissolved in water. Copy the table and use your knowledge of exothermic and endothermic reactions to complete it.


Name of substance to be dissolved in water


Potassium chloride Calcium chloride


Sodium hydrogen carbonate Sodium carbonate


Starting


temperature (°C)


25 25 25 25


Temperature after dissolving (°C)


12 33 15 29


4. Look at the table below and answer the questions that follow. Reaction


Start temperature (0


A22 B20 C19


Endothermic or exothermic reaction?


C)


End temperature (0 33 16 24


a. Identify whether each reaction is exothermic or endothermic. Justify your answer. b. Which reaction has the largest energy change?


5. Describe what would be observed when a thermometer is placed in an exothermic reaction. 6. Describe what an energy profile diagram is used to show.


7. Draw an energy profile diagram for: a. an endothermic reaction b. an exothermic reaction


8. Fig. 23.9 shows an energy profile diagram for a reaction.


a. Identify whether this is an exothermic or endothermic reaction. Justify your answer.


b. Copy the energy profile diagram and label the following parts of the diagram: products; reactants; activation energy; energy change during the reaction.


9. Explain, using an energy profile diagram, how a catalyst affects the rate of a reaction.


Reaction progress :Fig. 23.9


10. During a thunderstorm, lightning strikes could cause the following reaction to take place if the activation energy is reached:


nitrogen + oxygen  nitrogen oxide


a. Identify the reactants in this reaction. b. Identify the products in this reaction. c. The reaction is endothermic. Draw an energy profile diagram for this reaction. d. Explain the term ‘activation energy’.


C)


228 Elements of Science


Energy


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