Q45 of 152 Page 21

The chemical equations are balanced to satisfy one of the following laws in chemical reactions. This law is known as:

In a chemical reaction law of conservation of mass is followed.

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43 Which of the following is not an endothermic reaction? 44 One of the following is an exothermic reaction. This is: 46 When the solution of substance X is added to a solution of potassium iodide, then a yellow solid separates out from the solution.

(a) What do you think substance X is likely to be?


(b) Name the substance which the yellow solid consists of.


(c) Which characteristic of chemical reactions is illustrated by this example ?


(d) Write a balanced chemical equation for the reaction which takes place. Mention the physical states of all the reactants and products involved in the chemical equation.

 47 When water is added gradually to a white solid X, a hissing sound is heard and a lot of heat is produced forming a product Y. A suspension of Y in water is applied to the walls of a house during white washing. A clear solution of Y is also used for testing carbon dioxide gas in the laboratory.

(a) What could be solid X? Write its chemical formula.


(b) What could be product Y? Write its chemical formula.


(c) What is the common name of the solution of Y which is used for testing carbon dioxide gas?


(d) Write chemical equation of the reaction which takes place on adding water to solid X.


(e) Which characteristic of chemical reactions is illustrated by this example?