Question

9. Given the following bond enthalpies, calculate the AHxn for the following reaction. 1. C2H4 + 302 > 2cO2 + 2H20 BOND C-H С-О о-н 0-0 с-с Bond Enthalpy (kJ/mol) 413 799 463 495 614 10. Match the following molecules with their type of bonding: non-polar covalent, polar covalent, or ionic. a. MgCl2 b. HClc. Clz

Answer 1

9 Ans.

The reaction given is

$C_{2}H_{4}+ 3O_{2}\rightarrow 2CO_{2}+ 2H_{2}O$

Figure out how many bonds are broken and how many bonds are formed.

4 C-H bonds are broken

1 C=C bond is also broken

1 O=O bond per molecule is broken in 3 molecules of O₂ (that is 3 O=O bonds are broken)

2 C=O bonds are formed in 1 molecule of CO₂. So, in two molecules of CO₂, the no. of C=O bonds formed is 4

2 O-H bond is formed per molecule of H₂O. So, the number of O-H bonds formed in two molecules of H₂O is 4

The enthalpy change of the reaction is

$\Delta H_{rxn}= H_{b}-H_{f}$

where H_b = sum of bond enthalpies of the bonds broken

H_f = sum of bond enthalpies of the bonds formed

Therefore,

$\Delta H_{rxn}= [4(413)+614+3(495)]kJ/mol-[4(799)+4(463)]kJ/mol$

$\Delta H_{rxn}= [1652+614+1485]kJ/mol-[3196+1852]kJ/mol$

ΔΗ,rn-3751kJ/mol-5048kJ/mol TR

$\Delta H_{rxn}= -1297 kJ/mol$

Therefore, the enthalpy of the reaction is -1297kJ/mol

10 Ans.

MgCl₂ has ionic bonding because the bonds are formed by the transfer of electrons from Mg to Cl.

HCl is covalent because the bond is formed by the sharing of an electron each from both the atoms. It is polar because the atoms have different electronegativities.

Cl₂ is also covalent because the bond is formed by the sharing of electrons between the two atoms. It is non polar because there is no difference in electronegativities since both are Cl atom.