Q: Which of the following is the correct formula for percent yield?

$$\frac{\text{Actual yield}}{\text{Theoretical yield}} \times 100\%$$

Question 1

Which of the following best describes the greenhouse effect as illustrated in the provided diagram?

Accepted Answer

Greenhouse gases trap some of the heat radiated from Earth's surface, preventing it from escaping into space.

Question 2

Based on the atmospheric carbon dioxide graph, what trend is observed from 1860 to 2020?

Accepted Answer

Atmospheric CO$$_2$$ concentration has increased significantly, especially after 1960.

Question 3

Which of the following is a correct balanced equation for the complete combustion of methane, including physical states?

Accepted Answer

$$\mathrm{CH_4(g) + 2\ O_2(g) \rightarrow CO_2(g) + 2\ H_2O(l)}$$

Question 4

If 4.0 moles of A react with 4.0 moles of B in the reaction $$2A + 3B \rightarrow C$$, which reactant is limiting?

Accepted Answer

B is limiting because 4.0 mol is available but 6.0 mol is needed.

Question 5

Given the reaction $$2H_2(g) + O_2(g) \rightarrow 2H_2O(l)$$, how many grams of water are produced from 4.0 g of H$$_2$$ and 32.0 g of O$$_2$$?

Accepted Answer

36.0 g

Question 6

Which of the following statements about balancing chemical equations is correct?

Accepted Answer

You balance equations by changing the coefficients in front of compounds.

Question 7

A reaction mixture contains 45.10 g Fe$$_2O$_3$$ and 29.56 g CO. According to the equation $$\mathrm{Fe_2O_3(s) + 3CO(g) \rightarrow 2Fe(s) + 3CO_2(g)}$$, what is the mass of the excess reactant remaining after the reaction is complete?

Accepted Answer

Fe$$_2O$_3 is in $$excess; calculate the remaining mass after CO is consumed.

Question 8

Which of the following best explains why the actual yield of a chemical reaction is often less than the theoretical yield?

Accepted Answer

Side reactions and incomplete reactions reduce the actual yield.

Question 9

Methanol (CH$$_3OH) is $$produced by reacting CO and H$$_2. If 68.5 kg CO $$reacts with 8.60 kg H$$_2$$, what is the theoretical yield of methanol (in grams)? (Molar masses: CO = 28.01 g/mol, H$$_2 = 2.02 g/$$mol, CH$$_3OH = 32.05 g/$$mol)

Accepted Answer

Theoretical yield is determined by the limiting reactant, which is H$$_2.$$

Question 10

Which of the following is the correct formula for percent yield?

Accepted Answer

$$\frac{	ext{Actual yield}}{	ext{Theoretical yield}} 	imes 100\%$$

Question 11

In the reaction $$\mathrm{N_2(g) + 3H_2(g) \rightarrow 2NH_3(g)}$$, how many grams of NH$$_3$$ can be formed from 2.50 g N$$_2$$ and 2.00 g H$$_2$$? (Molar masses: N$$_2 = 28.02 g/$$mol, H$$_2 = 2.02 g/$$mol, NH$$_3 = 17.03 g/$$mol)

Accepted Answer

The limiting reactant is H$$_2$$; calculate moles of H$$_2$$ and use stoichiometry to find grams of NH$$_3.$$

Question 12

Which of the following is NOT a greenhouse gas?

Accepted Answer

N$$_2$$

Question 13

If equal masses of A and B are reacted in the equation $$A + 5B \rightarrow 3C + 4D$$, which is the limiting reactant if the molar mass of A is less than that of B?

Accepted Answer

B is limiting.

Question 14

Which of the following reaction mixtures would produce the greatest amount of water according to $$2H_2 + O_2 \rightarrow 2H_2O$$?

Accepted Answer

2 mol H$$_2$$ and 1 mol O$$_2$$

Question 15

A pizza recipe requires 1 crust, 5 oz tomato sauce, and 2 cups cheese per pizza. If you have 4 crusts, 15 oz tomato sauce, and 10 cups cheese, what is the limiting reactant and how many pizzas can you make?

Accepted Answer

Tomato sauce is limiting; 3 pizzas can be made.

Question 16

Which of the following best describes a stoichiometric mixture?

Accepted Answer

A mixture where all reactants are present in the exact ratios given by the balanced equation.

Question 17

What is the correct sequence of steps for solving a stoichiometry problem involving masses of reactants and products?

Accepted Answer

Balance equation → Convert mass to moles → Use mole ratio → Convert moles to mass

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