Endothermic and Exothermic Reactions - Matching Pairs Worksheet ... - Free Printable

Here are the correct matches for the questions on your worksheet. I have worked through each one to ensure the logic fits the definitions of energy changes in chemistry.

Step-by-step Matching:

1. Question: During a chemical reaction what is always transferred?
* Reasoning: In every chemical change, bonds break and new ones form. This process always involves moving energy around.
* Match: D - Energy

2. Question: Described what is meant by the "conservation of energy"
* Reasoning: This scientific law states that energy cannot be created out of nothing or destroyed into nothing; it just changes forms.
* Match: H - In a chemical reaction energy cannot be created or destroyed.

3. Question: How is energy transferred in chemical reactions?
* Reasoning: Energy moves because old bonds in the reactants break (which takes energy) and new bonds in the products form (which releases energy).
* Match: M - Through the breaking of chemical bonds in the reactants and creating new bonds in the products

4. Question: What name is given to reactions that transfer energy to the surroundings?
* Reasoning: "Exo" means out. These reactions push heat energy out into the air or container.
* Match: I - Exothermic

5. Question: How do you know that an exothermic reaction has taken place?
* Reasoning: Since the reaction releases heat, the temperature of the mixture will go up.
* Match: F - Through an increase in temperature from the reactants to the products.

6. Question: What is the name given to chemical reactions that transfer energy from the surroundings to the reactants?
* Reasoning: "Endo" means in. These reactions suck heat energy in from the outside.
* Match: B - Endothermic

7. Question: Name 2 examples of an exothermic reaction.
* Reasoning: Burning things (combustion), breathing (respiration), and neutralizing acids all release heat.
* Match: K - oxidation, combustion, respiration or neutralisation

8. Question: Name 2 examples of an endothermic reaction
* Reasoning: Plants making food (photosynthesis) and breaking down compounds with heat (thermal decomposition) need energy input.
* Match: C - photosynthesis, sodium hydrogen carbonate and citric acid or thermal decomposition

9. Question: What is meant by the term "thermal decomposition"?
* Reasoning: "Thermal" means heat and "decomposition" means breaking down. It literally means using heat to break something apart.
* Match: G - To break down with heat.

10. Question: If a reaction gives out energy to the surroundings, what happens to the energy of the products?
* Reasoning: If the reaction pushes energy *out*, the final products must have less stored energy than the starting ingredients.
* Match: A - The energy of the products will be less.

11. Question: Not every collision between particles results in a chemical reaction. Why?
* Reasoning: Particles need to hit each other hard enough (with enough energy) to break bonds. If they hit too softly, nothing happens.
* Match: L - Not all particles collide with enough energy to cause a reaction.

12. Question: What investigation would you do to find out if a reaction is endothermic or exothermic?
* Reasoning: You need to measure the temperature before you start and after you finish to see if it went up or down.
* Match: N - Record initial temperature of reactants and the final temperature to find a temperature difference.

13. Question: When you put sherbet into your mouth your mouth feels slightly cool. Why?
* Reasoning: Feeling cool means heat is leaving your mouth. The sherbet is absorbing that heat to make the reaction happen.
* Match: E - During this reaction heat is being removed from the surroundings.

14. Question: What is meant by a "reversible" reaction?
* Reasoning: A reversible reaction can go forward (reactants to products) and backward (products back to reactants).
* Match: J - A reaction that can revert back to the original reactants.

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Final Answer:
1-D, 2-H, 3-M, 4-I, 5-F, 6-B, 7-K, 8-C, 9-G, 10-A, 11-L, 12-N, 13-E, 14-J