What mass of natural gas (ch4) must you burn to emit 268 kj of heat? ch4(g)+2o2(g)→co2(g)+2h2o(g)δh∘rxn= −802.3kj express the mass in grams to three significant figures?

From the balanced equation, we can see that 1 mole of CH4 releases 802.3 kJ of heat upon combustion. The mass of 1 mole of CH4 is:

mass CH4 = 16.04 grams

So by ratio and proportion:

mass required = (-268 kJ) / (-802.3 kJ / 16.04 grams)

mass required = 0.334 grams