Question

(1)Write the ionic and the net ionic equations for the following chemical reaction:

Mg(OH)₂ + Na₂CO₃  MgCO₃ + 2 NaOH

(2)

Calculate the quantity of heat absorbed by 50.0 kg of rocks (SpH=0.82 J/g-K)

if their temperature increases by 12.0 K.

(3) Calculate the heat of formation of 10.4 g of KCl via the reaction

   2KClO₃  2KCl_(s) + O₂       ΔH = -89.4 Kj

Answer 1

1. The ionic equation: Mg(OH)₂ + 2Na⁺ + CO₃^2- Mg²⁺ + CO₃^2- + 2Na⁺ + 2OH^-

The net ionic equation: Mg(OH)₂ Mg²⁺ + 2OH^-

2. The heat (Q) absorbed by certain mass (in grams) of compounds if its temperature increases by T can be written as follows.

Q = m*c*T, c = specific heat = 0.82 J/g-K

i.e. Q = 5000 g * 0.82 J/g-K * 12 K = 492 KJ

3. Given that 2KClO₃(s) 2KCl(s) + 3O₂(g); ΔH = -89.4 KJ

Formation of 2 moles of KCl releases the heat of 89.4 KJ.

The given amount of KCl = 10.4 g = 10.4 g/74.6 g mol^-1 = 0.1394 mol

Therefore, the heat of formation of reaction = (0.1394/2) * (-89.4) KJ = -6.23 KJ