Question

Q9. For each of the following chemical and physical changes carried out at constant pressure, state whether work is done by the system on the surroundings or by the surroundings on the system, or whether the amount of work is negligible. State whether process or reaction is endothermic or exothermic.

A.benzene (l) → benzene (g)  

B. ½ N₂(g) + 3/2 H₂(g) → NH₃(g) ΔH = -92 kJ/mol

C. 2NH₄NO₃(s) → 2N₂(g) + 4H₂O(g) + O₂(g) + heat

D. H₂(g) + Cl₂(g) → 2HCl(g) + heat

E. CaCO₃(s) + 178 kJ/mol → CaO + CO₂ (g)

Answer 1

A)

Liquid is changing to gas.

So, volume is increasing.

Work is done by system on surrounding.

When liquid changes to gas, heat is absorbed.

So, this is endothermic

Answer: Work is done by system on surrounding, endothermic

B)

There are more gases on reactant than product.

So, volume is decreasing.

Work is done on system by surrounding.

delta H is negative, heat is released.

So, this is exothermic

Answer: Work is done on system by surrounding, exothermic

C)

There are gas on product side

So, volume is increasing.

Work is done by system on surrounding.

Heat is part of product. So, heat is released

So, this is exothermic

Answer: Work is done by system on surrounding, exothermic

D)

Number of gases is same on both sides.

So, the work is negligible.

Heat is part of product. So, heat is released

So, this is exothermic

Answer: work is negligible, exothermic

E)

There are gas on product side

So, volume is increasing.

Work is done by system on surrounding.

Heat is part of reactant. So, heat is absorbed

So, this is endothermic

Answer: Work is done by system on surrounding, endothermic