RPAL Cheat Sheet 2026

The 30 highest-yield RPAL facts, distilled from real exam questions. Print it, save it as a PDF, or study it here — free, no sign-up.

1. Which quantity is always equal before and after a chemical reaction in a closed system? → Total mass
2. What is the mole ratio of aluminum (Al) to aluminum oxide (Al₂O₃) in the reaction 4Al + 3O₂ → 2Al₂O₃? → 4:2
3. Which of the following is NOT a step in identifying the limiting reagent? → Calculating the percent yield of the reaction
4. A reaction between hydrogen and chlorine produces HCl. If 2 g of H₂ reacts with 71 g of Cl₂, what mass of HCl is produced? → 73 g
5. In the balanced equation 2H₂ + O₂ → 2H₂O, what is the mole ratio of H₂ to H₂O? → 2:2 (or 1:1)
6. In a chemical reaction, what is the definition of a product? → A substance that is formed as a result of the reaction
7. If 4 moles of a reactant produce 8 moles of a product, what is the mole ratio of reactant to product? → 1:2
8. What is a reactant in a chemical reaction? → A substance that undergoes change during a reaction
9. A balanced chemical equation demonstrates conservation of mass because: → It has the same number of atoms of each element on both sides
10. For the reaction 2Al + 3Cl₂ → 2AlCl₃, if 0.6 mol Al and 0.6 mol Cl₂ are used, which is the limiting reagent? → Cl₂
11. What does stoichiometry primarily deal with in a chemical reaction? → The quantitative relationships between reactants and products
12. What assumption underlies the theoretical yield calculation? → The reaction proceeds to completion with 100% conversion of limiting reagent to product
13. A student finds a theoretical yield of 15 g but collects only 15 g of product. What is notable about this result? → The percent yield is 100%, which is extremely rare in practice
14. If the limiting reagent is fully consumed, what happens to the excess reagent? → Some of it remains unreacted (leftover)
15. For C₃H₈ + 5O₂ → 3CO₂ + 4H₂O, what is the mole ratio of C₃H₈ to CO₂? → 1:3
16. For 4Fe + 3O₂ → 2Fe₂O₃, if 2 mol O₂ is the limiting reagent, what is the theoretical yield of Fe₂O₃? → 4/3 mol ≈ 1.33 mol
17. If both reactants are used up completely in a reaction, what can you conclude? → They were in a perfect stoichiometric ratio with no excess
18. A student reports that after a reaction, 0.5 mol of the excess reagent remains. What does this tell you about the reaction? → The reaction went to completion with the limiting reagent fully consumed
19. Why is percent yield almost always less than 100%? → Because of side reactions, product loss during purification, and incomplete reactions
20. A mole ratio can be written as either A/B or B/A. Which form do you use? → The form that cancels the unit you want to eliminate and gives the unit you want
21. In industrial chemistry, why is maximizing percent yield important? → It reduces waste and lowers production costs per unit of product
22. For 2KClO₃ → 2KCl + 3O₂, if 2 mol KClO₃ decomposes, what is the theoretical yield of O₂? → 3 mol O₂
23. For 3H₂ + N₂ → 2NH₃, how many moles of N₂ are needed to produce 6 mol NH₃? → 3 mol N₂
24. For the reaction 2HCl + Ca → CaCl₂ + H₂, if 4 mol HCl and 3 mol Ca are used, what is the excess reagent and how much remains? → Ca; 1 mol remains
25. A reaction with a theoretical yield of 10 g gives only 2 g of product. What is the percent yield, and how might a chemist improve it? → 20%; improve by minimizing side reactions and product loss
26. A reaction yields 0.45 mol of product but the theoretical yield is 0.50 mol. What is the percent yield? → 90%
27. For N₂ + 3H₂ → 2NH₃, if H₂ is limiting at 6 mol, what is the theoretical yield of NH₃? → 4 mol
28. Why is it useful to calculate the amount of excess reagent remaining? → To know what leftover materials are present after the reaction
29. Which reagent is used to calculate theoretical yield? → The limiting reagent
30. For CaCO₃ → CaO + CO₂, if 100 g of CaCO₃ (molar mass = 100 g/mol) reacts completely, what is the theoretical yield of CO₂ (molar mass = 44 g/mol)? → 44 g