In an endothermic reaction, gaseous water decomposes to form hydrogen and oxygen gas.

2H2O (g) > 2H2 (g) + O2 (g) ∆H = 483.6 kJ

If the ∆H decreases to 241.8 kJ, how many grams of gaseous water decomposed?

18 g of gaseous water

Explanation:

We are given the equation;

2H2O (g) > 2H2 (g) + O2 (g) ∆H = 483.6 kJ

We are required to determine the mass of gaseous water decomposed when the amount of heat absorbed is 241.8 kJ.

From the equation;

2 moles of water are decomposed when 483.6 kJ is absorbed

Therefore;

241.8 kJ will be absorbed to decompose;

 = (2 × 241.8 kJ) ÷ 483.6 kJ

= 1 mole

But; molar mass of water is 18 g /mol

Therefore;

Mass of gaseous water decomposed is 18 g