Stoichiometry - AP Chemistry

1. What is the first step in a stoichiometry problem?

   Write a balanced chemical equation. Ensures atom conservation for stoichiometric calculations.

2. How many moles of $H_2$ are needed to produce 2 moles of $NH_3$ in $N_2 + 3H_2 \rightarrow 2NH_3$?

   3 moles. 3:2 mole ratio from balanced equation coefficients.

3. Calculate the percent composition of oxygen in $H_2O$.

   88.81%. Oxygen mass ($16$) divided by $H_2O$ mass ($18$) $\times 100\%$.

4. Find the molar mass of $CO_2$.

   44 g/mol. Carbon (12) + 2 oxygen atoms (16 each) = 44 g/mol.

5. Identify the unit for molar mass.

   grams per mole (g/mol). Standard unit expressing mass per mole of substance.

6. Which unit is used to express concentration in stoichiometry?

   Molarity (M). Standard concentration unit for solution calculations.

7. Calculate the molarity of a solution with 10 moles in 5 L.

   2 M. $\frac{10 \text{ moles}}{5 \text{ L}} = 2$ M concentration.

8. Identify the limiting reactant in 4 moles $N_2$ and 10 moles $H_2$ for $N_2 + 3H_2 \rightarrow 2NH_3$.

   $H_2$. Need 12 moles $H_2$ but only have 10; $H_2$ limits.

9. What is the stoichiometric coefficient for $H_2$ in $2H_2 + O_2 \rightarrow 2H_2O$?

   2. Coefficient shows 2 molecules react in balanced equation.

10. What is the molar mass of $H_2SO_4$?

    98.1 g/mol. 2H (2) + S (32) + 4O (64) = 98 g/mol total.

11. Which unit is used to express concentration in stoichiometry?

    Molarity (M). Standard concentration unit for solution calculations.

12. What is the molecular formula for a compound with empirical formula $CH_2O$ and molar mass 180 g/mol?

    $C_6H_{12}O_6$. $180 \div 30 = 6$, so multiply $CH_2O$ by 6.

13. What is the molecular formula for a compound with empirical formula $CH_2O$ and molar mass 180 g/mol?

    $C_6H_{12}O_6$. $180 \div 30 = 6$, so multiply $CH_2O$ by 6.

14. What is the concentration of a solution with 5 moles of solute in 2 L of solution?

    2.5 M. $\frac{5 \text{ moles}}{2 \text{ L}} = 2.5$ M concentration.

15. Determine the empirical formula for a compound with 40% carbon, 6.7% hydrogen, and 53.3% oxygen.

    $CH_2O$. Convert percentages to moles, then find simplest ratio.

16. How is actual yield different from theoretical yield?

    Actual yield is the measured amount of product obtained. Theoretical assumes perfect conditions; actual is experimental.

17. How is theoretical yield calculated?

    Use stoichiometry from the balanced equation. Assumes complete reaction with limiting reactant consumed.

18. What is the formula to calculate the number of particles from moles?

    $\text{particles} = \text{moles} \times 6.022 \times 10^{23}$. Multiplies moles by Avogadro's number for particle count.

19. Find the moles of $H_2O$ in 36 grams.

    2 moles. $36 \div 18 = 2$ using $H_2O$ molar mass of 18 g/mol.

20. Identify the limiting reactant in 4 moles $N_2$ and 10 moles $H_2$ for $N_2 + 3H_2 \rightarrow 2NH_3$.

    $H_2$. Need 12 moles $H_2$ but only have 10; $H_2$ limits.

21. Calculate the number of molecules in 2 moles of $H_2$.

    $1.204 \times 10^{24}$ molecules. $2 \times 6.022 \times 10^{23}$ molecules per mole.

22. Convert 3 moles of $NaCl$ to grams.

    175.5 grams. $3 \times 58.5 = 175.5$ using $NaCl$ molar mass.

23. Calculate the percent composition of oxygen in $H_2O$.

    88.81%. Oxygen mass (16) divided by $H_2O$ mass (18) × 100%.

24. How do you calculate mass from moles?

    $\text{mass (g)} = \text{moles} \times \text{molar mass (g/mol)}$. Multiplies moles by molar mass to get mass in grams.

25. What is the stoichiometric coefficient for $H_2$ in $2H_2 + O_2 \rightarrow 2H_2O$?

    2. Coefficient shows 2 molecules react in balanced equation.

26. Determine the empirical formula for a compound with 40% carbon, 6.7% hydrogen, and 53.3% oxygen.

    $CH_2O$. Convert percentages to moles, then find simplest ratio.

27. Determine the moles of $NaOH$ needed to neutralize $1$ mole of $HCl$.

    $1$ mole. $1:1$ mole ratio from balanced acid-base equation.

28. Determine the limiting reactant in $2H_2 + O_2 \rightarrow 2H_2O$ given 5 moles $H_2$ and 2 moles $O_2$.

    $H_2$. Needs 2.5 moles $O_2$, but only 2 available, so $H_2$ limits.

29. Define molar mass.

    The mass of one mole of a substance in grams. Equals the atomic/molecular weight expressed in g/mol.

30. Find the volume of gas at STP for 1 mole.

    22.4 L. Standard molar volume at 0°C and 1 atm pressure.

31. What is the first step in a stoichiometry problem?

    Write a balanced chemical equation. Ensures atom conservation for stoichiometric calculations.

32. What is the molecular formula for a compound with empirical formula $CH_2O$ and molar mass 180 g/mol?

    $C_6H_{12}O_6$. $180 \div 30 = 6$, so multiply $CH_2O$ by 6.

33. Calculate the mass of 0.5 moles of $C_6H_{12}O_6$.

    90 grams. $0.5 \times 180 = 90$ using glucose molar mass.

34. How is theoretical yield calculated?

    Use stoichiometry from the balanced equation. Assumes complete reaction with limiting reactant consumed.

35. What is the excess reactant in $2H_2 + O_2 \rightarrow 2H_2O$ with 5 moles $H_2$ and 2 moles $O_2$?

    $O_2$. Remains after limiting reactant is completely consumed.

36. How do you calculate mass from moles?

    $\text{mass (g)} = \text{moles} \times \text{molar mass (g/mol)}$. Multiplies moles by molar mass to get mass in grams.

37. Determine the moles of $NaOH$ needed to neutralize 1 mole of $HCl$.

    1 mole. 1:1 mole ratio from balanced acid-base equation.

38. Convert 0.25 moles of $Mg$ to atoms.

    $1.505 \times 10^{23}$ atoms. $0.25 \times 6.022 \times 10^{23}$ atoms per mole.

39. Calculate the number of molecules in 2 moles of $H_2$.

    $1.204 \times 10^{24}$ molecules. $2 \times 6.022 \times 10^{23}$ molecules per mole.

40. What is empirical formula?

    The simplest whole-number ratio of atoms. Shows simplest ratio without molecular complexity.

41. What is the percent yield if the theoretical yield is 100g and actual yield is 80g?

    80%. $\frac{80}{100} \times 100\% = 80\%$ efficiency.

42. Which unit is used to express concentration in stoichiometry?

    Molarity (M). Standard concentration unit for solution calculations.

43. Find the moles of $H_2O$ in 36 grams.

    2 moles. $36 \div 18 = 2$ using $H_2O$ molar mass of 18 g/mol.

44. What is the formula for molarity?

    $\text{Molarity (M)} = \frac{\text{moles of solute}}{\text{liters of solution}}$. Relates amount of solute to solution volume.

45. Convert 3 moles of $NaCl$ to grams.

    175.5 grams. $3 \times 58.5 = 175.5$ using $NaCl$ molar mass.

46. Calculate the volume at STP for 0.5 moles of gas.

    11.2 L. $0.5 \times 22.4 = 11.2$ liters at STP.

47. Find the molar mass of $CO_2$.

    44 g/mol. Carbon (12) + 2 oxygen atoms (16 each) = 44 g/mol.

48. Calculate the mass of 0.5 moles of $C_6H_{12}O_6$.

    90 grams. $0.5 \times 180 = 90$ using glucose molar mass.

49. What is the formula to calculate the number of moles from mass?

    $\text{moles} = \frac{\text{mass (g)}}{\text{molar mass (g/mol)}}$. Divides mass by molar mass to find amount in moles.

50. Determine the limiting reactant in $2H_2 + O_2 \rightarrow 2H_2O$ given 5 moles $H_2$ and 2 moles $O_2$.

    $H_2$. Needs 2.5 moles $O_2$, but only 2 available, so $H_2$ limits.

51. What is the concentration of a solution with 5 moles of solute in 2 L of solution?

    2.5 M. $\frac{5 \text{ moles}}{2 \text{ L}} = 2.5$ M concentration.

52. Calculate the mass of 0.5 moles of $C_6H_{12}O_6$.

    90 grams. $0.5 \times 180 = 90$ using glucose molar mass.

53. How is actual yield different from theoretical yield?

    Actual yield is the measured amount of product obtained. Theoretical assumes perfect conditions; actual is experimental.

54. How many moles of $H_2$ are needed to produce 2 moles of $NH_3$ in $N_2 + 3H_2 \rightarrow 2NH_3$?

    3 moles. 3:2 mole ratio from balanced equation coefficients.

55. Identify the unit for molar mass.

    grams per mole (g/mol). Standard unit expressing mass per mole of substance.

56. Find the volume of gas at STP for 1 mole.

    22.4 L. Standard molar volume at 0°C and 1 atm pressure.

57. Identify the unit for molar mass.

    grams per mole (g/mol). Standard unit expressing mass per mole of substance.

58. How is theoretical yield calculated?

    Use stoichiometry from the balanced equation. Assumes complete reaction with limiting reactant consumed.

59. What is the excess reactant in $2H_2 + O_2 \rightarrow 2H_2O$ with 5 moles $H_2$ and 2 moles $O_2$?

    $O_2$. Remains after limiting reactant is completely consumed.

60. What is the excess reactant in $2H_2 + O_2 \rightarrow 2H_2O$ with 5 moles $H_2$ and 2 moles $O_2$?

    $O_2$. Remains after limiting reactant is completely consumed.

61. How do you calculate mass from moles?

    $\text{mass (g)} = \text{moles} \times \text{molar mass (g/mol)}$. Multiplies moles by molar mass to get mass in grams.

62. Determine the moles of $NaOH$ needed to neutralize 1 mole of $HCl$.

    1 mole. $1:1$ mole ratio from balanced acid-base equation.

63. Determine the empirical formula for a compound with 50% sulfur and 50% oxygen by mass.

    $SO_2$. Equal mass percentages give 1:2 atomic ratio S:O.

64. Identify the limiting reactant in 4 moles $N_2$ and 10 moles $H_2$ for $N_2 + 3H_2 \rightarrow 2NH_3$.

    $H_2$. Need 12 moles $H_2$ but only have 10; $H_2$ limits.

65. What is the formula for percent yield?

    $\text{Percent yield} = \frac{\text{actual yield}}{\text{theoretical yield}} \times 100$. Compares actual to theoretical yield as a percentage.

66. Determine the limiting reactant in $2H_2 + O_2 \rightarrow 2H_2O$ given 5 moles $H_2$ and 2 moles $O_2$.

    $H_2$. Needs 2.5 moles $O_2$, but only 2 available, so $H_2$ limits.

67. What is the formula to calculate the number of moles from mass?

    $\text{moles} = \frac{\text{mass (g)}}{\text{molar mass (g/mol)}}$. Divides mass by molar mass to find amount in moles.

68. What is the stoichiometric coefficient for $H_2$ in $2H_2 + O_2 \rightarrow 2H_2O$?

    2. Coefficient shows 2 molecules react in balanced equation.

69. What is the formula for molarity?

    $\text{Molarity (M)} = \frac{\text{moles of solute}}{\text{liters of solution}}$. Relates amount of solute to solution volume.

70. What is the formula to calculate the number of particles from moles?

    $\text{particles} = \text{moles} \times 6.022 \times 10^{23}$. Multiplies moles by Avogadro's number for particle count.

71. How many grams of $O_2$ are needed to react with 4 moles of $C$ in $C + O_2 \rightarrow CO_2$?

    128 grams. $4 \times 32 = 128$ grams using 1:1 mole ratio.

72. How many moles of $H_2$ are needed to produce 2 moles of $NH_3$ in $N_2 + 3H_2 \rightarrow 2NH_3$?

    3 moles. 3:2 mole ratio from balanced equation coefficients.

73. What is empirical formula?

    The simplest whole-number ratio of atoms. Shows simplest ratio without molecular complexity.

74. What is the percent yield if the theoretical yield is 100g and actual yield is 80g?

    80%. $\frac{80}{100} \times 100\% = 80\%$ efficiency.

75. State Avogadro's number.

    $6.022 \times 10^{23}$. The number of particles in one mole of any substance.

76. What is the formula for molarity?

    $\text{Molarity (M)} = \frac{\text{moles of solute}}{\text{liters of solution}}$. Relates amount of solute to solution volume.

77. State Avogadro's number.

    $6.022 \times 10^{23}$. The number of particles in one mole of any substance.

78. What is the molar mass of $H_2SO_4$?

    98.1 g/mol. 2H (2) + S (32) + 4O (64) = 98 g/mol total.

79. Calculate the volume at STP for 0.5 moles of gas.

    11.2 L. $0.5 \times 22.4 = 11.2$ liters at STP.

80. What is the first step in a stoichiometry problem?

    Write a balanced chemical equation. Ensures atom conservation for stoichiometric calculations.

81. Determine the empirical formula for a compound with 50% sulfur and 50% oxygen by mass.

    $SO_2$. Equal mass percentages give 1:2 atomic ratio S:O.

82. Determine the empirical formula for a compound with 40% carbon, 6.7% hydrogen, and 53.3% oxygen.

    $CH_2O$. Convert percentages to moles, then find simplest ratio.

83. Convert 3 moles of $NaCl$ to grams.

    175.5 grams. $3 \times 58.5 = 175.5$ using $NaCl$ molar mass.

84. Find the molar mass of $CO_2$.

    44 g/mol. Carbon (12) + 2 oxygen atoms (16 each) = 44 g/mol.

85. What is the purpose of a mole ratio in stoichiometry?

    To convert between moles of different substances. Uses coefficients from balanced equations for conversions.

86. Find the moles of $H_2O$ in 36 grams.

    2 moles. $36 \div 18 = 2$ using $H_2O$ molar mass of 18 g/mol.

87. What is the purpose of a mole ratio in stoichiometry?

    To convert between moles of different substances. Uses coefficients from balanced equations for conversions.

88. What is the formula for percent yield?

    $\text{Percent yield} = \frac{\text{actual yield}}{\text{theoretical yield}} \times 100$. Compares actual to theoretical yield as a percentage.

89. Find the volume of 3 moles of gas at STP.

    67.2 L. $3 \times 22.4 = 67.2$ liters at standard conditions.

90. What is the molar mass of $H_2SO_4$?

    98.1 g/mol. 2H (2) + S (32) + 4O (64) = 98 g/mol total.

91. How is actual yield different from theoretical yield?

    Actual yield is the measured amount of product obtained. Theoretical assumes perfect conditions; actual is experimental.

92. Calculate the molarity of a solution with 10 moles in 5 L.

    2 M. $\frac{10 \text{ moles}}{5 \text{ L}} = 2$ M concentration.

93. What is the concentration of a solution with 5 moles of solute in 2 L of solution?

    2.5 M. $\frac{5 \text{ moles}}{2 \text{ L}} = 2.5$ M concentration.

94. Define molar mass.

    The mass of one mole of a substance in grams. Equals the atomic/molecular weight expressed in g/mol.

95. Calculate the volume at STP for 0.5 moles of gas.

    11.2 L. $0.5 \times 22.4 = 11.2$ liters at STP.

96. Determine the empirical formula for a compound with 50% sulfur and 50% oxygen by mass.

    $SO_2$. Equal mass percentages give 1:2 atomic ratio S:O.

97. What is the percent yield if the theoretical yield is 100g and actual yield is 80g?

    80%. $\frac{80}{100} \times 100\% = 80\%$ efficiency.

98. What is the formula to calculate the number of moles from mass?

    $\text{moles} = \frac{\text{mass (g)}}{\text{molar mass (g/mol)}}$. Divides mass by molar mass to find amount in moles.

99. What is empirical formula?

    The simplest whole-number ratio of atoms. Shows simplest ratio without molecular complexity.

100. What is the purpose of a mole ratio in stoichiometry?

     To convert between moles of different substances. Uses coefficients from balanced equations for conversions.

101. Define molar mass.

     The mass of one mole of a substance in grams. Equals the atomic/molecular weight expressed in g/mol.

102. What is the formula for percent yield?

     $\text{Percent yield} = \frac{\text{actual yield}}{\text{theoretical yield}} \times 100$. Compares actual to theoretical yield as a percentage.

103. Calculate the percent composition of oxygen in $H_2O$.

     88.81%. Oxygen mass (16) divided by $H_2O$ mass (18) × 100%.

104. What is the formula to calculate the number of particles from moles?

     $\text{particles} = \text{moles} \times 6.022 \times 10^{23}$. Multiplies moles by Avogadro's number for particle count.

105. State Avogadro's number.

     $6.022 \times 10^{23}$. The number of particles in one mole of any substance.

106. Calculate the number of molecules in 2 moles of $H_2$.

     $1.204 \times 10^{24}$ molecules. $2 \times 6.022 \times 10^{23}$ molecules per mole.

Study these flashcards