Question 12 -14 When 1.0 mole of ZnO changes into pure Zinc and oxygen, the A H

Question

Question 12 -14 When 1.0 mole of ZnO changes into pure Zinc and oxygen, the A H -348 kJ. What does this tell you about the reaction? the formation of pure zinc and oxygen from Zno releases heat energy 2 the formation of pure zinc and oxygen from ZnO requires energy 3) the reaction is exothermic pure zinc and oxygen are lower energy chemicals than ZnO is. Question 13 Look at this reaction Which is not true? -1 4 2H20(0 2H2(8) +02(g) H 560 k Heat energy is given off during the reaction The products are higher energy than the reactants The enthalpy change is positive 4 This reaction is endothermic

Explanation / Answer

The delta H or delta H° of a reaction is the heat change or the enthalpy change of the reaction which is equal to the difference of the enthalpy change of products and the reactants. When the reaction results with the production of heat than the delta H value is negative and such reactions are called exothermic reactions. For such reactions, the products are lower in energy than the reactants. But, if the reaction absorbs or requires heat or energy then the delta H value is positive and such reactions are called endothermic reactions. For such reactions, the products are higher in energy than the reactants.

12. It is given that the delta H value is 348 kJ, a positive value. This means that the reaction requires energy and so it is an endothermic reactions. Therefore, the correct option is (2).

13. Here, delta H° is 560 kJ. This means:

Thus, the statement which is not true is (1).

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