Consider the formation of gaseous magnesium oxide from elemental gaseous magnesium and oxygen.

1) Write the chemical equation of this reaction.

2) Determine the overall change in energy for the formation of gaseous magnesium oxide.

3) Does this formation release or absorb energy? Explain.

4) Would it require more energy to melt CO (s) or MgO (s)? Explain.

Data:

I₁ (Mg) = 1.23 aJ

I₂ (Mg) = 2.41 aJ

EA₁ (O) = -0.234 aJ

EA₂ (O) = 1.30 aJ

k = 231 aJ.pm

r_Mg2+ = 72 pm

r_O2- = 140 pm

Question

Consider the formation of gaseous magnesium oxide from elemental gaseous magnesium and oxygen.

1) Write the chemical equation of this reaction.

2) Determine the overall change in energy for the formation of gaseous magnesium oxide.

3) Does this formation release or absorb energy? Explain.

4) Would it require more energy to melt CO (s) or MgO (s)? Explain.

Data:

I₁ (Mg) = 1.23 aJ

I₂ (Mg) = 2.41 aJ

EA₁ (O) = -0.234 aJ

EA₂ (O) = 1.30 aJ

k = 231 aJ.pm

r_Mg2+ = 72 pm

r_O2- = 140 pm

| General Chemistry 1

Accepted Answer

1) Mg (g) + O (g) → MgO (g)

2)

First step:

Mg (g) → Mg⁺ (g) + 1 e^-

Mg⁺ (g) → Mg²⁺ (g) + 1 e^-

Energy = I₁ + I₂ = 1.23 + 2.41 = 3.64 aJ

Second step:

O (g) + 1 e^- → O^- (g)

O^- (g) + 1 e^- → O^2- (g)

Energy = EA₁ + EA₂ = 1.07 aJ

Third step:

Mg²⁺ (g) + O^2- (g) → MgO (g)

Energy = E_coulomb = 231 x $\frac{(+ 2) (- 2)}{212}$ = -4.36 aJ

Energy of reaction: E = 3.64 + 1.07 – 4.36 = 0.35 aJ

3) E > 0 ⇒ absorb energy

4) CO(s) ⇒ covalent bonding

MgO (s) ⇒ ionic bonding

ionic compound has higher melting point than covalent compound.

Midterm 2 - Question 1 | General Chemistry 1