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Free Limiting and Excess Reactants MCQs with Answers

17 Limiting and Excess Reactants MCQs from Chemistry, each with the correct answer and a written explanation of why it is correct. Free and unlimited, with no account needed.

Limiting and excess reactants are identified from the balanced chemical equation and the available amounts of each substance. The limiting reactant determines the maximum product formed, while the excess reactant remains after completion, so questions require mole ratios, theoretical yield and sometimes percentage yield calculations.

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17 questions

1. The limiting reactant in a chemical reaction is the one that

  • A. is present in the largest amount by mass
  • B. is completely used up first and so determines the amount of product formed
  • C. has the highest molar mass
  • D. remains unreacted at the end

Explanation: The reaction stops when one reactant runs out, so that reactant fixes the maximum yield no matter how much of the others is present.

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Correct answer: is completely used up first and so determines the amount of product formed

2. In the reaction N2 + 3H2 gives 2NH3, if 1 mole of nitrogen is mixed with 2 moles of hydrogen, the limiting reactant is

  • A. nitrogen, because it has the larger molar mass
  • B. neither, because both are used up exactly
  • C. hydrogen, because 3 moles would be needed to react with 1 mole of nitrogen
  • D. nitrogen, because fewer moles of it are present

Explanation: The equation demands three moles of hydrogen for every mole of nitrogen, so 1 mole of nitrogen would need 3 moles of hydrogen and only 2…

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Correct answer: hydrogen, because 3 moles would be needed to react with 1 mole of nitrogen

3. In the reaction 2H2 + O2 gives 2H2O, 4 moles of hydrogen are mixed with 3 moles of oxygen. The amount of the excess reactant left over is

  • A. 2 moles of hydrogen
  • B. 3 moles of oxygen
  • C. nothing, both are exactly consumed
  • D. 1 mole of oxygen

Explanation: Four moles of hydrogen require only two moles of oxygen, so hydrogen is limiting and 3 minus 2, that is 1 mole of oxygen, remains…

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Correct answer: 1 mole of oxygen

4. The mass of P4O10 that will be obtained from the reaction of 1.33 gram of P4 and 5.07 of oxygen is___________?

  • A. 2.05 gram
  • B. 3.05 gram
  • C. 4.05 gram
  • D. 5.05 gram

Explanation: The balanced reaction is P4 + 5O2 -> P4O10. Moles of P4 = 1.33 g ÷ 123.9 g/mol = 0.0107 mol, while the 5.07 g O2 provides 5.07 g ÷ 32.0…

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Correct answer: 3.05 gram

5. A limiting reactant is one which________________?

  • A. is taken in lesser quantity in grams as compared to other reactants
  • B. is taken in lesser quantity in volume as compared to other reactants
  • C. gives the maximum amount of the product which is required
  • D. gives the minimum amount of the product under consideration

Explanation: The limiting reactant is consumed first according to the balanced equation, so it determines the maximum, or minimum possible under the…

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Correct answer: gives the minimum amount of the product under consideration

6. In the absence of a catalyst, ammonia burns in an excess of oxygen to produce steam and nitrogen. What is the volume of oxygen remaining when 60 cm³ of ammonia is burnt in 100 cm³ of oxygen, all volumes being measured at the same temperature and pressure?

  • A. 35 cm³
  • B. 40 cm³
  • C. 45 cm³
  • D. 55 cm³

Explanation: 4NH3 + 3O2→ 6H2O + 2N2 60 cm³ 100 cm³ : Given (22,400 × 4) cm³ of ammonia uses (22,400 × 3) cm³ of O2 1 cm³ of ammonia uses .75 cm³ of O2…

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Correct answer: 55 cm³

7. The reactant which is consumed completely in a reaction is known as the _ reactant.

  • A. Fractional
  • B. Initial
  • C. Limiting
  • D. Minor

Explanation: The reactant that is in the least amount in the reaction and consumed first is called the limiting reactant.

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Correct answer: Limiting

8. The reactant which is consumed completely in a reaction is known as a _ reactant.

  • A. Fractional
  • B. Initial
  • C. Limiting
  • D. Minor

Explanation: A limiting reactant is a reactant that is present in the smallest amount in a reaction and therefore limits the amount of product that can…

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Correct answer: Limiting

9. Ten moles of hydrogen are allowed to react with 6 moles of oxygen. How much water will be obtained from reaction on complete consumption of one gas?

  • A. 10 moles.
  • B. 8 moles.
  • C. 6 moles.
  • D. 4 moles.

Explanation: Balance chemical equation2H2 + O2 -> 2H20Now we will compare the moles of H2 and O2 with water from the balanced chemical equation.H2…

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Correct answer: 10 moles.

10. A limiting reactant is the one which:

  • A. Is mostly a cheaper substance and taken in larger quantity
  • B. Is consumed earlier and controls the amount of product formed in a chemical reaction
  • C. Gives greatest number of moles of products
  • D. Is left behind after the completion of reaction

Explanation: Explanation: A limiting reactant is the one which is consumed earlier and controls the amount of product formed in a chemical reaction.

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Correct answer: Is consumed earlier and controls the amount of product formed in a chemical reaction

11. If 28.0g nitrogen gas is reacted with 8.0g of hydrogen gas to form ammonia, the limiting reactant among the two will be:

  • A. N2
  • B. H2
  • C. both (a) & (b)
  • D. None of these

Explanation: The balanced chemical equation for the production of ammonia is: N2 + 3H2 → 2NH3.

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Correct answer: N2

12. lf 28.0g nitrogen gas is reacted with 8.0g of hydrogen gas to form Ammonia, the limiting reactant among the two will be:

  • A. N2
  • B. H2
  • C. Both a & b
  • D. None of them

Explanation: The balanced chemical equation for the formation of ammonia (NH3) is:N2 + 3H2 → 2NH3You start with 28.0 g of N2 and 8.0 g of H2.

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Correct answer: N2

13. N2 + 3H2 → 2NH3In the above reaction, the limiting reagent is:

  • A. N2
  • B. H2
  • C. Ammonia
  • D. None of the above

Explanation: The balanced equation is shown below. N2 (g)+ 3H2 (g) → 2NH3 (g) If equal moles of each reactant are used, hydrogen will be the limiting…

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Correct answer: H2

14. 2XeF6 + SiO2 --> 2XeOF4 + SiF4 Consider the above chemical reaction. If 122.6 g of XeF6 reacts with 60 g of SiO2 to form the products. Select the limiting reagent and amount of SiF4 formed: (XeF6 245.3 amu, SiO2 = 60 amu, SiF4 = 104 amu)

  • A. XeF6, 25.5 g
  • B. SiO2, 26 g
  • C. XeF6, 52 g
  • D. SiO2, 52 g

Explanation: To solve this problem, first calculate the moles of each reactant. For XeF6, with a molar mass of 245.3 g/mol, 122.6 g is equivalent to…

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Correct answer: XeF6, 25.5 g

15. A container containing two moles of liquid ethanol and four moles of oxygen gas were sparked together to form CO2 & H2O. Identify the heating reagent?

  • A. Oxygen gas
  • B. Liquid ethanol
  • C. Both A and B
  • D. None of the above

Explanation: The heating reagent in this reaction is oxygen gas. When ethanol and oxygen gas are sparked together, they undergo a combustion reaction…

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Correct answer: Oxygen gas

16. A container containing two moles of liquid ethanol and the gas of oxygen gas was sparked together to form CO2 & HO2-Identify the limiting reagent?

  • A. Liquid ethanol
  • B. Oxygen gas
  • C. Both (A) and (B)
  • D. None of the stove

Explanation: So, in the reaction between liquid ethanol and oxygen gas, we need to figure out which one is the limiting reagent.

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Correct answer: Liquid ethanol

17. Consider the reaction below, if 5 moles each of hydrogen and oxygen are reacted to form water, the reaction reveals:2H2 + O2 --> 2H2O

  • A. H2 is the excess agent
  • B. O2 is the limiting agent
  • C. H2 is the limiting reagent
  • D. The reaction has no limiting reagent

Explanation: Option C is the correct answer. In the reaction 2H2 + O2 --> 2H2O, we start with 5 moles of both hydrogen and oxygen.

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Correct answer: H2 is the limiting reagent
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