In the reaction C + 2 H2 → CH4, mix 12.0 g carbon (1.00 mol) with 5.00 g H2 (2.50 mol). Which reactant is limiting and how many moles of CH4 can form?

• A. Limiting: H2; CH4 formed: 1.25 mol
• B. Limiting: C; CH4 formed: 1.00 mol
• C. Limiting: C; CH4 formed: 2.00 mol
• D. Limiting: H2; CH4 formed: 0.50 mol

Answer: (B)

To solve this, focus on identifying the limiting reagent by comparing what each reactant can supply to meet the reaction’s stoichiometry. The reaction uses 1 mole of carbon for every 2 moles of hydrogen to produce 1 mole of methane. The amounts given are about 1.00 mole of carbon and 2.50 moles of hydrogen. To consume all the carbon you’d need 2.00 moles of hydrogen, but you have 2.50 moles, which means hydrogen is more than enough. The carbon runs out first, so it is the limiting reagent. Since the reaction yields methane in a 1:1 ratio with carbon, the amount of methane formed is also 1.00 mole.