Which of the following processes has a positive value for ΔE and which are endothermic? i. A system absorbs 50 kJ of heat from the surroundings and does 30 kJ of work on the surroundings. ii. A system releases 25 kJ of heat into the surroundings and 45 kJ of work is done on the system. iii. q = 12.5 kJ, w = – 3500 J

Explanation:

According to conservation of energy

q = ΔE + w

q is heat given , ΔE is increase in internal energy and w is work done by the gas.

i )

q = 50 kJ ; w = 30 kJ

Substituting the values

50 kJ = ΔE + 30 kJ

ΔE = 20 kJ ; Hence ΔE is positive.

ii )

q = - 25 kJ ; w = 45 kJ

- 25 kJ = ΔE + 45 kJ

ΔE = - 70 kJ .

ΔE is negative. It is endothermic.

iii )

q = 12.5 kJ ; w = - 3.5 kJ

12.5 kJ = ΔE - 3.5 kJ

ΔE = 16 kJ

Hence ΔE is positive.

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