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Chemical Reactions Energy Worksheet

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Chemical Reactions Energy Worksheet

Finn and Ruben investigate energy changes in reactions. Read each task carefully. For questions asking you to explain, include evidence from the information given.

Track the energy

A reaction is exothermic when energy is transferred from the reacting chemicals to the surroundings. An endothermic reaction transfers energy from the surroundings to the reacting chemicals.

1.In an exothermic reaction, thermal energy is transferred from the reacting chemicals to the surroundings. What happens to the thermal energy of the surroundings, and what temperature change would support your answer?

2.A sealed reaction vessel becomes colder while a reaction occurs. Which conclusion is best supported?

The reaction is endothermic because it takes in energy from its surroundings.
The reaction is exothermic because it releases energy to its surroundings.
No energy is transferred because the vessel is sealed.
The reaction must be combustion.

3.Complete the statement: In an endothermic reaction, energy is by the reacting chemicals, and the surroundings usually become .

4.Classify each process as mainly exothermic or endothermic: (a) burning fuel in a heater; (b) photosynthesis; (c) cooking an egg; (d) a hand warmer releasing heat.

(a) Burning fuel in a heater
(b) Photosynthesis
(c) Cooking an egg
(d) A hand warmer releasing heat

Endothermic
Exothermic
Endothermic
Exothermic

Investigate the evidence

Finn tests two reactions in identical cups. The starting temperature is 20°C in both trials. The temperature is measured one minute after mixing.

Trial

Starting temperature

Temperature after 1 minute

20°C

27°C

20°C

14°C

5.Use the temperature results to classify Trial A and Trial B. State the temperature change for each trial.

6.Why is it useful to start both trials at the same temperature and use identical cups?

7.True or false: A temperature rise during a reaction is evidence that energy has been transferred to the surroundings.

TrueFalse

Explain and apply

Use word equations to show the starting substances on the left and the products on the right of the arrow.

8.Zinc reacts with copper sulfate to form zinc sulfate and copper. Write the word equation, then identify the reactants.

9.Hydrogen peroxide breaks down into water and oxygen. Complete the word equation: hydrogen peroxide → + .

10.Ruben says, “If a reaction is endothermic, it will keep going only while it receives energy.” Is this always true? Explain the difference between energy needed to start a reaction and the overall energy change.

11.A safety briefing explains that burning fuel can release heat and start fires. Give one practical fire-safety action and explain how knowing the reaction releases energy supports that action.