Q. 24

# A plate of area 1

Given

Surface area of the plate, A = 10 cm2 = 10 × 10−4 m2

Thickness of copper deposited, t = 10 μm = 10−5 m

Density of copper = 9000 kg/m3

Electrochemical equivalent of copper –3 × 10–7 kg C–1

specific heat capacity of water – 4200 J kg–1 K–1

Volume, V of copper deposited,

V = (2t)

Where

A is the area of the plates

t is the thickness of the plates

Putting the values in the above formula, we get

We know, mass of copper deposited,

m = Volume × Density

m = ZQ

where

m = mass of the substance

Q= charge

Z= Electrochemical equivalent

Putting the values in the above formula, we get
18 × 10−5 = 3 × 10−7 × Q

Q = 6 × 102 C

Now,

The energy spent by the cell will be = Work done by the cell

W = V× Q

Where

V is the potential difference

Q is the charge

Putting the values in the above formula, we get

= 12 × 6 × 102

= 72 × 102 = 7.2 kJ

Let us take ∆θ as the rise in temperature of water.

If this amount of energy is used to heat 100 g of water, then-

Q = c×m ×∆θ

Where,

c= specific heat of water

Q= Heat

m = mass of water

∆θ = change in temperature

Substituting

7.2 × 103 = 100 × 10−3 × 4200 × ∆θ

θ = 17 K

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