Consider the given balanced chemical equation: 2H2 + O2 gives 2H2O. If 4 g of H2 reacts with 32 g of O2 to produce 28 g of H2O, what is the percentage yield of the reaction? (Molar mass of H2 = 2 g/mol, O2 = 32 g/mol and H2O = 18 g/mol)
Correct answer: B. 77.8%
- A. 63.6%
- B. 77.8%
- C. 87.5%
- D. 92.5%
Explanation
Four grams of hydrogen is 2 moles and 32 g of oxygen is 1 mole, which is exactly the 2 to 1 ratio the equation requires, so neither is in excess and 2 moles of water should form, that is 36 g. The percentage yield is therefore 28 divided by 36 multiplied by 100, which is 77.8 per cent. Checking for a limiting reactant before computing the theoretical yield is the step most often skipped.
This question appeared on the UHS MDCAT 2025 paper, which you can sit online with every answer explained.
Report an error
The more specific you are, the faster it gets fixed. A source beats an opinion.
Prefer email? support@testustad.com
About Theoretical and Percentage Yield
Theoretical yield is the maximum product predicted from a balanced equation and the amount of limiting reactant. Work includes identifying the limiting reagent, comparing theoretical and actual yield, and calculating percentage yield using stoichiometric mole relationships.
Practise Fundamental Concepts of Chemistry
894 free Fundamental Concepts of Chemistry MCQs from Chemistry, each with the correct answer and an explanation. Unlimited attempts, no account needed.
Discussion
Stuck on an option, or know a faster way to get there? Ask or explain it here.
No comments yet. Be the first to explain this one.
Exams that ask Chemistry questions like this
Chemistry is on 14 papers prepared for on TestUstad, and all of them draw the same bank, so this question is worth knowing for every one of them.
More Theoretical and Percentage Yield questions
How many grams of calcium oxide are produced when 1 mole of calcium carbonate decomposes completely, given CaCO3 gives CaO + CO2?
The actual yield of a reaction is usually less than the theoretical yield for all of the following reasons EXCEPT
A reaction has a theoretical yield of 25 g but only 20 g of product is obtained. The percentage yield is
A chemical reaction has a theoretical yield of 25 g, but only 20 g of product was obtained. What is the percentage yield of the reaction?
If % yield and actual yield is 80 and 20 g respectively, what will be theoretical yield?
The theoretical yield is, when % yield and actual yied are 55% and 24g respectively: