Q: Which of the following reactions is endothermic?

$A + \text{heat} \rightarrow B + C$

Q: Which formula is used to determine the whole number multiple for converting an empirical formula to a molecular formula?

$\text{whole number multiple} = \frac{\text{molecular weight}}{\text{empirical formula weight}}$

Question 1

Which statement best describes the meaning of the coefficients in a balanced chemical equation?

Accepted Answer

They indicate the number of moles of each compound involved in the reaction.

Question 2

Given the balanced equation $2 \mathrm{Fe} (s) + 3 \mathrm{Cl}_2 (g) \rightarrow 2 \mathrm{FeCl}_3 (s)$, how many moles of $\mathrm{Cl}_2$ are required to react completely with 4 moles of iron?

Accepted Answer

6 moles

Question 3

In the combustion of butane, $2 \mathrm{C}_4\mathrm{H}_{10} + 13 \mathrm{O}_2 \rightarrow 8 \mathrm{CO}_2 + 10 \mathrm{H}_2\mathrm{O}$, how many moles of water are produced when 0.5 moles of butane are burned?

Accepted Answer

5 moles

Question 4

A student decomposes 2.00 g of ammonium bicarbonate ($\mathrm{NH}_4\mathrm{HCO}_3$). How many grams of ammonia ($\mathrm{NH}_3$) are produced? (Molar mass $\mathrm{NH}_4\mathrm{HCO}_3 = 79.056$ g/mol, $\mathrm{NH}_3 = 17.031$ g/mol)

Accepted Answer

0.430 g

Question 5

Which of the following reactions is endothermic?

Accepted Answer

$A + 	ext{heat} ightarrow B + C$

Question 6

A compound is found to contain 42.88% carbon and 57.12% oxygen by mass. What is its empirical formula?

Accepted Answer

$\mathrm{CO}$

Question 7

Vitamin C contains 40.92% C, 4.58% H, and 54.50% O by mass. What is the empirical formula of vitamin C?

Accepted Answer

$\mathrm{C}_3\mathrm{H}_4\mathrm{O}_3$

Question 8

If the empirical formula of a compound is $\mathrm{C}_3\mathrm{H}_4\mathrm{O}_3$ and its molecular weight is 176 amu, what is its molecular formula? (Empirical formula weight = 88 amu)

Accepted Answer

$\mathrm{C}_6\mathrm{H}_8\mathrm{O}_6$

Question 9

Which step is NOT part of the process for determining an empirical formula from percent composition?

Accepted Answer

Multiply the ratios by the atomic number of each element.

Question 10

A reaction produces heat as a product. What type of reaction is this?

Accepted Answer

Exothermic

Question 11

For the reaction $2 \mathrm{C}_4\mathrm{H}_{10} + 13 \mathrm{O}_2 \rightarrow 8 \mathrm{CO}_2 + 10 \mathrm{H}_2\mathrm{O}$, what is the mole ratio of $\mathrm{O}_2$ to $\mathrm{CO}_2$?

Accepted Answer

13:8

Question 12

A sample contains 20.0 g of $\mathrm{C}_4\mathrm{H}_{10}$. How many moles of $\mathrm{CO}_2$ are produced when it is completely combusted? (Molar mass $\mathrm{C}_4\mathrm{H}_{10} = 58.12$ g/mol)

Accepted Answer

2.75 moles $\mathrm{CO}_2$

Question 13

Which formula is used to determine the whole number multiple for converting an empirical formula to a molecular formula?

Accepted Answer

$	ext{whole number multiple} = \frac{	ext{molecular weight}}{	ext{empirical formula weight}}$

Question 14

A compound has an empirical formula of $\mathrm{CH}_2$ and a molecular weight of 56 g/mol. What is its molecular formula? (Empirical formula weight = 14 g/mol)

Accepted Answer

$\mathrm{C}_4\mathrm{H}_8$

Question 15

Which of the following best describes a stoichiometric relationship in a chemical reaction?

Accepted Answer

The mole ratios between reactants and products as given by the coefficients in a balanced equation.

Question 16

A student analyzes a compound and finds it contains 24.0 g of C, 4.0 g of H, and 32.0 g of O. What is the empirical formula?

Accepted Answer

$\mathrm{C}_2\mathrm{H}_4\mathrm{O}$

Question 17

If a reaction is exothermic, which of the following is true?

Accepted Answer

The reaction releases heat to the surroundings.

Question 18

Which of the following is the correct sequence for determining an empirical formula from percent composition?

Accepted Answer

Convert percent to grams, convert grams to moles, divide by smallest number of moles, round to whole numbers.

Question 19

A sample of $\mathrm{NH}_4\mathrm{HCO}_3$ is heated and produces 0.430 g of $\mathrm{NH}_3$. How many grams of $\mathrm{NH}_4\mathrm{HCO}_3$ were decomposed? (Molar mass $\mathrm{NH}_4\mathrm{HCO}_3 = 79.056$ g/mol, $\mathrm{NH}_3 = 17.031$ g/mol)

Accepted Answer

2.00 g

Stoichiometry and Empirical/Molecular Formulas: Quantitative Information from Balanced Equations

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