Study the reactions for the formation of compounds from their elements. I. C(s) + O2(g) → CO2(g) ΔHf = −394 kJ II. H2(g) + 12O2(g) → H2O(l) ΔHf = −242 kJ III. 2C(s) + 3H2(g) → C2H6(g) ΔH =−84 kJ The combustion of C2H6 is shown by the following equation: C2H6(g) + 72O2(g) → 2CO2(g) + 3H2O(l) Which option correctly gives the enthalpy of combustion of 0.2 moles of C2H6(g)? −1,430 kJ 286 kJ −286 kJ 1,430 kJ Exam 3 Click on the numbers to jump from one question to another. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

The correct option is -286 kJ

Explanation:

The given parameters are

C(s) + O₂(g) → CO₂(g)   ΔHf = -394 kJ

H₂(g) + 12O₂(g)→H₂O ΔHf = -242 kJ

2C(s) + 3H₂(g)→C₂H₆(g)  ΔH = -84 kJ

Te given equation is C₂H₆(g) + 7/2O₂(g) →2CO₂(g) + 3H₂O(l)

The heat of formation or enthalpy of combustion = Heat of formation of the products - Heat of formation of the reactants

The enthalpy of combustion of the reaction = 2*(-394) + 3*(-242)- ((-84)+7/2*0)) = -1,430 kJ

Given that the reaction consists of one mole of C₂H₆(g), we have;

The enthalpy of combustion of one mole of C₂H₆(g) = -1,430 kJ

Therefore, the enthalpy of combustion of 0.2 mole of C₂H₆(g) = -1,430 kJ × 0.2 = -286 kJ

The correct option = -286 kJ.

hydrocarbons are organic compounds that contain only hydrogens and carbons. they can be saturated (those which contain only carbon-carbon single bonds) or unsaturated (those which contain carbon-carbon double or triple bonds) in nature. hydrocarbons can undergo several reactions like substitution, elimination etc.  

on substituting one or more hydrogen atoms in hydrocarbon it results in the formation of haloalkane. as the halogen atoms are large compared to the carbon and hydrogen atoms, due to which the molecular weight increases and the bond become polar because of presence electronegative halogen atom and results in the increase in boiling point of the haloalkane.

thus, the correct option is (b) that is the boiling point of the new compound increases on substituting a hydrogen atom with a halogen in a hydrocarbon.