19.1 Which of the following statements are correct? (Note: more than one stateme

Question

19.1 Which of the following statements are correct? (Note: more than one statement may be correct) (a) When the liquid and vapour phases of a substance co-exist the pressure depends only on the volume, not the tempera- ture. (b) When the temperature of a substance is less than the criti- cal temperature there is a distinct phase change between the liquid and solid phases involving latent heat. (c) The latent heat for the vaporisation of water is greater at 0 °C than at 100°C (d) When two objects (1 and 2) exchange heat, the correspond- ing heat quantities, Q1 and Q2, satisfy the equation Q1 = Q2. (e) The specific heat capacity of a substance is numerically the same as the amount of thermal energy required to increase the temperature of 2kg of the substance by 0.5°C.

Explanation / Answer

a)correct

degree of freedom at that point

F = C-P+2

F = degree of freedom

C = no. of components

P = no. of phases

F = 1 - 2(vapour and liquid)+2

=1 and hence it will depend only on one variable

b)

correct,after critical point they are indistinguishable

c)

correct, heat of vaporization decreases with temperature

d)

false, it may or may not be,depends upon other factors such as work done

e)

correct

Cp =kJ/kg.oC heat capacity = amount of energy required to change the temperature of 1kg substant to 1 oC

or 2kg x 0.5 oC = 1kg.oC

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