Q: Which of the following is a correct example of a dimensional analysis setup to convert 5.0 moles of H$$_2O to $$molecules?

$$5.0\ \mathrm{mol} \times \dfrac{6.022 \times 10$$^{23}$$\ \mathrm{molecules}}{1\ \mathrm{mol}}$$

Q: A reaction has a percent yield of 80%. If the theoretical yield is 25.0 g, what is the actual yield?

$$\dfrac{80}{100} \times 25.0\ \mathrm{g} = 20.0\ \mathrm{g}$$

Q: Which of the following is the correct formula for calculating molarity?

$$\mathrm{Molarity\ (M) = \dfrac{\text{moles\ of\ solute}}{\text{liters\ of\ solution}}}$$

Question 1

Which of the following statements about significant figures is correct when multiplying 2.50 (3 sig figs) by 0.040 (2 sig figs)?

Accepted Answer

The answer should have 2 significant figures.

Question 2

A student mixes aqueous solutions of Na$$_2SO$_4$$ and BaCl$$_2. $$What is the net ionic equation for the formation of a precipitate?

Accepted Answer

$$\mathrm{Ba$$^{2+}$$(aq) + SO_4$^{2-}(aq) \rightarrow $$BaSO_4$$(s)}$$

Question 3

Which of the following best describes an oxidation reaction?

Accepted Answer

A reaction in which a substance loses electrons.

Question 4

If 0.500 mol of HCl is dissolved in enough water to make 1.00 L of solution, what is the molarity of the solution?

Accepted Answer

$$0.500\ \mathrm{M}$$

Question 5

Which of the following is the correct balanced chemical equation for the combustion of methane ($$\mathrm{CH_4$}$$)?

Accepted Answer

$$\mathrm{CH_4$ + 2O_2 \rightarrow CO_2$ + 2H_2O}$$

Question 6

A solution contains 0.20 mol of NaCl in 500 mL of water. What is the molarity of NaCl in the solution?

Accepted Answer

$$0.40\ \mathrm{M}$$

Question 7

Which of the following statements about Avogadro's number is correct?

Accepted Answer

It is the number of atoms in one mole of any element.

Question 8

A student wants to convert 3.00 g of carbon ($$\mathrm{C}) to $$moles. What is the correct calculation using the molar mass of carbon ($$12.01\ \mathrm{g/mol}$$)?

Accepted Answer

$$\dfrac{3.00\ \mathrm{g}}{12.01\ \mathrm{g/mol}} = 0.250\ \mathrm{mol}$$

Question 9

Which of the following is a correct example of a dimensional analysis setup to convert 5.0 moles of H$$_2O to $$molecules?

Accepted Answer

$$5.0\ \mathrm{mol} 	imes \dfrac{6.022 	imes 10$$^{23}$$\ \mathrm{molecules}}{1\ \mathrm{mol}}$$

Question 10

Which of the following best describes a strong acid in aqueous solution?

Accepted Answer

It completely dissociates into ions.

Question 11

A reaction has a percent yield of 80%. If the theoretical yield is 25.0 g, what is the actual yield?

Accepted Answer

$$\dfrac{80}{100} 	imes 25.0\ \mathrm{g} = 20.0\ \mathrm{g}$$

Question 12

Which of the following is the correct formula for calculating molarity?

Accepted Answer

$$\mathrm{Molarity\ (M) = \dfrac{	ext{moles\ of\ solute}}{	ext{liters\ of\ solution}}}$$

Question 13

Which of the following statements about thermal equilibrium is correct?

Accepted Answer

It is the state in which two objects in contact have no net flow of heat between them.

Question 14

Which equation would you use to calculate the heat absorbed by a substance during a temperature change?

Accepted Answer

$$q = m c \Delta T$$

Question 15

A heating curve for water shows a plateau at 100$$^\circC. $$What does this plateau represent?

Accepted Answer

The phase change from liquid to gas (boiling).

Question 16

Which of the following is the correct formula for percent composition by mass?

Accepted Answer

$$\mathrm{\%\ composition = \dfrac{	ext{mass\ of\ element}}{	ext{total\ mass\ of\ compound}} 	imes 100}$$

Question 17

Which of the following best describes an endothermic reaction?

Accepted Answer

A reaction that absorbs heat from the surroundings.

Question 18

A sample contains 1.50 moles of Na atoms. How many atoms are present in the sample?

Accepted Answer

$$1.50\ \mathrm{mol} 	imes 6.022 	imes 10$$^{23}$$\ \mathrm{atoms/mol} = 9.03 	imes 10$$^{23}$$\ \mathrm{atoms}$$

Question 19

Which of the following is the correct empirical formula for a compound containing 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen by mass?

Accepted Answer

$$\mathrm{CH_2O}$$

General Chemistry Exam 3 Study Guide: Chemical Reactions, Stoichiometry, and Thermochemistry

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