Page 15 - NCERT Science Class 10 English Medium

Silver bromide also behaves in the same way.
Sunlight
2AgBr(s)  → 2Ag(s) + Br (g) (1.23)
2
The above reactions are used in black and white photography.
What form of energy is causing these decomposition reactions?
We have seen that the decomposition reactions require energy either
in the form of heat, light or electricity for breaking down the reactants.
Reactions in which energy is absorbed are known as endothermic
reactions.
Carry out the following Activity

Take about 2 g barium hydroxide in a test tube. Add 1 g of ammonium chloride and mix
with the help of a glass rod. Touch the bottom of the test tube with your palm. What do you
feel? Is this an exothermic or endothermic reaction?

Q U E S T I O N S

1. A solution of a substance ‘X’ is used for whitewashing.
(i) Name the substance ‘X’ and write its formula.
(ii) Write the reaction of the substance ‘X’ named in (i) above with ?
water.
2. Why is the amount of gas collected in one of the test tubes in Activity
1.7 double of the amount collected in the other? Name this gas.

1.2.3 Displacement Reaction

Activity 1.9
Activity 1.91.9
Activity 1.9
1.9
Activity
Activity
n Take three iron nails and clean them by
rubbing with sand paper.
n Take two test tubes marked as (A) and
(B). In each test tube, take about 10 mL
copper sulphate solution.
n Tie two iron nails with a thread and
immerse them carefully in the copper
sulphate solution in test tube B for
about 20 minutes [Fig. 1.8 (a)]. Keep one
iron nail aside for comparison.
n After 20 minutes, take out the iron nails
from the copper sulphate solution.
n Compare the intensity of the blue colour
of copper sulphate solutions in test tubes
(A) and (B) [Fig. 1.8 (b)].
n Also, compare the colour of the iron nails
Figure 1.8 dipped in the copper sulphate solution
(a) Iron nails dipped in copper sulphate solution with the one kept aside [Fig. 1.8 (b)].

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