Q: How many molecules are present in $$0.50$$ moles of $$\mathrm{CO}_2$$?

$$3.01 \times 10$$^{23}$$ molecules

Q: Which of the following is the correct formula to convert grams to moles?

$$\text{moles} = \dfrac{\text{grams}}{\text{molar mass}}$$

Question 1

Which of the following best describes a redox reaction?

Accepted Answer

A reaction in which electrons are transferred between substances.

Question 2

Given the reaction: $$2 \mathrm{Na} + 2 \mathrm{H}_2\mathrm{O} \rightarrow 2 \mathrm{NaOH} + \mathrm{H}_2$$, which element is oxidized?

Accepted Answer

Sodium ($$\mathrm{Na})$$

Question 3

Balance the following chemical equation: $$\mathrm{C}_2\mathrm{H}_6 + \mathrm{O}_2 \rightarrow \mathrm{CO}_2 + \mathrm{H}_2\mathrm{O}$$

Accepted Answer

$$2 \mathrm{C}_2\mathrm{H}_6 + 7 \mathrm{O}_2 \rightarrow 4 \mathrm{CO}_2 + 6 \mathrm{H}_2\mathrm{O}$$

Question 4

Which of the following is the correct definition of Avogadro's number?

Accepted Answer

The number of particles in one mole of a substance, $$6.022 	imes 10$$^{23}$$.

Question 5

How many molecules are present in $$0.50$$ moles of $$\mathrm{CO}_2$$?

Accepted Answer

$$3.01 	imes 10$$^{23}$$ molecules

Question 6

Which of the following reactions is an example of an exothermic reaction?

Accepted Answer

Combustion of methane: $$\mathrm{CH}_4 + 2 \mathrm{O}_2 \rightarrow \mathrm{CO}_2 + 2 \mathrm{H}_2\mathrm{O}$$

Question 7

What is the molar mass of $$\mathrm{Na}_2\mathrm{SO}_4$$?

Accepted Answer

$$142 \mathrm{g/mol}$$

Question 8

If $$4.00$$ grams of $$\mathrm{NaOH}$$ are dissolved in water, how many moles of $$\mathrm{NaOH}$$ are present? ($$\mathrm{NaOH}$$ molar mass = $$40.0 \mathrm{g/mol})$$

Accepted Answer

$$0.100$$ moles

Question 9

A chemical reaction has the following equation: $$2 \mathrm{Al} + 3 \mathrm{Cl}_2 \rightarrow 2 \mathrm{AlCl}_3. If $$you start with $$5.0$$ grams of $$\mathrm{Al}$$ and excess $$\mathrm{Cl}_2$$, how many grams of $$\mathrm{AlCl}_3$$ can be produced? ($$\mathrm{Al}$$ molar mass = $$27.0 \mathrm{g/mol}$$, $$\mathrm{AlCl}_3$$ molar mass = $$133.5 \mathrm{g/mol})$$

Accepted Answer

$$24.7$$ grams

Question 10

Which of the following best describes the limiting reactant in a chemical reaction?

Accepted Answer

The reactant that is completely consumed first, limiting the amount of product formed.

Question 11

In the reaction $$2 \mathrm{H}_2 + \mathrm{O}_2 \rightarrow 2 \mathrm{H}_2\mathrm{O}$$, if you have $$4$$ moles of $$\mathrm{H}_2$$ and $$2$$ moles of $$\mathrm{O}_2$$, what is the limiting reactant?

Accepted Answer

Neither, both are exactly enough for complete reaction.

Question 12

Which of the following is the correct formula to convert grams to moles?

Accepted Answer

$$	ext{moles} = \dfrac{	ext{grams}}{	ext{molar mass}}$$

Question 13

A student mixes $$10.0$$ grams of $$\mathrm{CaCO}_3$$ with $$10.0$$ grams of $$\mathrm{HCl} in $$the reaction $$\mathrm{CaCO}_3 + 2 \mathrm{HCl} \rightarrow \mathrm{CaCl}_2 + \mathrm{CO}_2 + \mathrm{H}_2\mathrm{O}. $$Which reactant is limiting? ($$\mathrm{CaCO}_3$$ molar mass = $$100.1 \mathrm{g/mol}$$, $$\mathrm{HCl}$$ molar mass = $$36.5 \mathrm{g/mol})$$

Accepted Answer

$$\mathrm{HCl}$$

Question 14

Which of the following is the correct definition of oxidation?

Accepted Answer

Loss of electrons by a substance.

Question 15

If $$2.00$$ moles of $$\mathrm{Fe}$$ react with $$3.00$$ moles of $$\mathrm{O}_2 to $$form $$\mathrm{Fe}_2\mathrm{O}_3$$ according to $$4 \mathrm{Fe} + 3 \mathrm{O}_2 \rightarrow 2 \mathrm{Fe}_2\mathrm{O}_3$$, what is the maximum number of moles of $$\mathrm{Fe}_2\mathrm{O}_3$$ that can be formed?

Accepted Answer

$$1.00$$ mole

Question 16

Which of the following statements about endothermic reactions is correct?

Accepted Answer

Endothermic reactions absorb energy from their surroundings.

Question 17

A reaction has a theoretical yield of $$15.0$$ grams, but only $$12.0$$ grams of product are obtained. What is the percent yield?

Accepted Answer

$$80.0\%$$

Question 18

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

Accepted Answer

$$	ext{Percent Yield} = \dfrac{	ext{Actual Yield}}{	ext{Theoretical Yield}} 	imes 100\%$$

Study Notes: Chemical Reactions and Quantities (General Chemistry)

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