Question

A.) When 1 mole of CO(g) reacts with Cl₂(g) to form COCl₂(g) according to the following equation, 108 kJ of energy are evolved.

CO(g) + Cl₂(g)---->COCl₂(g)

Is this reaction endothermic or exothermic? _________

What is the value of q?__________ kJ

B.) When 1 mole of CO(g) reacts with H₂O(l) to form CO₂(g) and H₂(g) according to the following equation, 2.80 kJ of energy are absorbed.

CO(g) + H₂O(l)---->CO₂(g) + H₂(g)

Is this reaction endothermic or exothermic? ______________

What is the value of q? __________ kJ

C.) Hydrocarbons, compounds containing only carbon and hydrogen, are important in fuels. The heat of combustion of cyclopentane, C₅H₁₀, is 786.6 kcal/mol.

Write a balanced equation for the complete combustion of cyclopentane.

__________+__________----> __________+__________

How much energy is released during the complete combustion of 392 grams of cyclopentane ? __________ kcal

Answer 1

A) Since heat is evolved, i.e. Heat is given out to the surroundings, the reaction is exothermic. It produces heat during the reaction.

The value of q in case of exothermic reactions is always negative.

Hence, value of q= - 108kj

B)Since in this case, energy is absorbed, instead of evolved, therefore the reaction is termed as endothermic i.e. Absorbing heat.

The value of q in endothermic reactions is always positive

Hence, value of q = +2.8 kJ

C) The balanced reaction is given as follows :

2C₅H₁₀ + 15O₂ ===> 10CO₂ + 10H₂O

We first need to calculate number of moles in 392 g of cyclopentane:

Molecular weight of cyclopentane = 70g / mol

Hence, moles = given weight / molecule weight = 392 / 70 = 5.6

Heat of combustion = moles * heat of combustion / mol = 5.6 * 786.6 kcal/mol = 4404.96 kcal