The combustion of 0.374 kg of methane in the presence of excess oxygen produces 0.983 kg of carbon dioxide. what is the percent yield?

Assuming that it undergoes complete combustion, all of the carbons from methane would be converted to carbon dioxide. Thus you would be able to know the % yield of product by converting everything first to moles then dividing the product with the reactant. The moles of methane is 0.023375 while the moles of carbon dioxide is 0.02234. In calculating for the % yield divide the moles of CO2 with moles of methane and you would get 95.58%. 

a gas, having a molecular weight of 13 kg/kmol and a kinematic viscosity of 0.25 cm2/s, flows through a pipe 0.25 m internal diameter and 5 km long at the rate of 0.4 m3/s and is delivered at atmospheric pressure.