How many degrees can 100 kg of water be heated by burning 300 g of natural gas

Q1 (natural gas combustion) = Q2 (water heating).

Q1 = q * m1, where q is the specific heat of combustion of natural gas (tabular value q = 4.4 * 10 ^ 7 J / kg), m1 is the mass of burnt natural gas (m1 = 300 g or 0.3 kg).

Q2 = C * m2 * Δt, where C is the specific heat capacity of water (tabular value C = 4200 J / (K * kg)), m2 is the mass of water for heating (m2 = 100 kg), Δt is the amount of water temperature rise.

q * m1 = C * m2 * Δt.

Δt = q * m1 / (C * m2) = 4.4 * 10 ^ 7 * 0.3 / (4200 * 100) ≈ 31.4 ºС.