# World of Chemistry

## Educators

Problem 1

Although mass is a property of matter we can conveniently measure in the laboratory, the coefficients of a balanced chemical equation are not directly interpreted on the basis of mass. Explain why.

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Problem 2

Explain why, in the balanced chemical equation $\mathrm{C}+\mathrm{O}_{2} \rightarrow \mathrm{CO}_{2},$ we know that 1 $\mathrm{g}$ of $\mathrm{C}$ will $\mathrm{not}$ react exactly with 1 $\mathrm{g}$ of $\mathrm{O}_{2}$ .

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Problem 3

For each of the following reactions, give the balanced equation for the reaction and state the meaning of the equation in terms of numbers of individual molecules and in terms of moles of molecules.
a. $\mathrm{NO}(g)+\mathrm{O}_{2}(g) \rightarrow \mathrm{NO}_{2}(g)$
b. $\mathrm{AgC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}(a q)+\mathrm{CuSO}_{4}(a q) \rightarrow$
$\quad \mathrm{Ag}_{2} \mathrm{SO}_{4}(s)+\mathrm{Cu}\left(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\right)_{2}(a q)$
c. $\mathrm{PCl}_{3}(l)+\mathrm{H}_{2} \mathrm{O}(l) \rightarrow \mathrm{H}_{3} \mathrm{PO}_{3}(l)+\mathrm{HCl}(g)$
d. $\mathrm{C}_{2} \mathrm{H}_{6}(g)+\mathrm{Cl}_{2}(g) \rightarrow \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{Cl}(g)+\mathrm{HCl}(g)$

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Problem 4

For each of the following reactions, give the balanced chemical equation for the reaction and state the meaning of the equation in terms of individual molecules and in terms of moles of molecules.
a. $\mathrm{MnO}_{2}(s)+\mathrm{Al}(s) \rightarrow \mathrm{Mn}(s)+\mathrm{Al}_{2} \mathrm{O}_{3}(s)$
b. $\mathrm{B}_{2} \mathrm{O}_{3}(s)+\mathrm{CaF}_{2}(s) \rightarrow \mathrm{BF}_{3}(g)+\mathrm{CaO}(s)$
c. $\mathrm{NO}_{2}(g)+\mathrm{H}_{2} \mathrm{O}(l) \rightarrow \mathrm{HNO}_{3}(a q)+\mathrm{NO}(g)$
d. $\mathrm{C}_{6} \mathrm{H}_{6}(l)+\mathrm{H}_{2}(g) \rightarrow \mathrm{C}_{6} \mathrm{H}_{12}(l)$

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Problem 5

True or false? For the reaction represented by the chemical equation
$$2 \mathrm{H}_{2} \mathrm{O}_{2}(a q) \rightarrow 2 \mathrm{H}_{2} \mathrm{O}(l)+\mathrm{O}_{2}(g)$$
if 2.0 $\mathrm{g}$ of hydrogen peroxide decomposes, then 2.0 $\mathrm{g}$ of water and 1.0 $\mathrm{g}$ of oxygen gas will be produced.

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Problem 6

Consider the balanced equation
$$\mathrm{CH}_{4}(g)+2 \mathrm{O}_{2}(g) \rightarrow \mathrm{CO}_{2}(g)+2 \mathrm{H}_{2} \mathrm{O}(g)$$
What is the mole ratio that would enable you to calculate the number of moles of oxygen needed to react exactly with a given number of moles of $\mathrm{CH}_{4}(g) ?$ What mole ratios would you use to calculate how many moles of each product form from a given number of moles of $\mathrm{CH}_{4} ?$

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Problem 7

Consider the unbalanced chemical equation
$$\mathrm{Ag}(s)+\mathrm{H}_{2} \mathrm{S}(g) \rightarrow \mathrm{Ag}_{2} \mathrm{S}(s)+\mathrm{H}_{2}(g)$$
Balance the equation. Identify the mole ratios that you would use to calculate the number of moles of each product that would form for a given number of moles of silver reacting.

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Problem 8

For each of the following unbalanced chemical equations, calculate how many moles of each product would be produced by the complete conversion of 0.125 mol of the reactant indicated in boldface. State clearly the mole ratio used for the conversion.
a. $\mathbf{F} \mathrm{e} \mathbf{O}(s)+\mathrm{C}(s) \rightarrow \mathrm{Fe}(l)+\mathrm{CO}_{2}(g)$
b. $\mathrm{Cl}_{2}(g)+\mathbf{K I}(a q) \rightarrow \mathrm{KCl}(a q)+\mathrm{I}_{2}(s)$
c. $\mathbf{N a}_{2} \mathbf{B}_{4} \mathbf{O}_{7}(s)+\mathrm{H}_{2} \mathrm{SO}_{4}(a q)+\mathrm{H}_{2} \mathrm{O}(l)-$
$\quad \mathrm{H}_{3} \mathrm{BO}_{3}(s)+\mathrm{Na}_{2} \mathrm{SO}_{4}(a q)$
d. $\mathbf{C a C}_{2}(s)+\mathrm{H}_{2} \mathrm{O}(l) \rightarrow$
$\quad \mathrm{Ca}(\mathrm{OH})_{2}(s)+\mathrm{C}_{2} \mathrm{H}_{2}(g)$

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Problem 9

For each of the following balanced chemical equations, calculate how many moles and how many grams of each product would be produced by the complete conversion of 0.50 mol of the reactant indicated in boldface. State clearly the mole ratio used for each conversion.
a. $\mathbf{N H}_{3}(g)+\mathrm{HCl}(g) \rightarrow \mathrm{NH}_{4} \mathrm{Cl}(s)$
b. $\mathrm{CH}_{4}(g)+4 \mathbf{S}(s) \rightarrow \mathrm{CS}_{2}(l)+2 \mathrm{H}_{2} \mathrm{S}(g)$
c. $\mathbf{P C l}_{3}(l)+3 \mathrm{H}_{2} \mathrm{O}(l) \rightarrow \mathrm{H}_{3} \mathrm{PO}_{3}(a q)+3 \mathrm{HCl}(a q)$
d. $\mathrm{NaOH}(s)+\mathrm{CO}_{2}(g) \rightarrow \mathrm{NaHCO}_{3}(s)$

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Problem 10

For each of the following unbalanced equations indicate how many moles of the first product are produced if 0.625 mol of the second product forms. State clearly the mole ratio used for each conversion.
a. $\mathrm{KO}_{2}(s)+\mathrm{H}_{2} \mathrm{O}(l) \rightarrow \mathrm{O}_{2}(g)+\mathrm{KOH}(s)$
b. $\mathrm{SeO}_{2}(g)+\mathrm{H}_{2} \mathrm{Se}(g) \rightarrow \operatorname{Se}(s)+\mathrm{H}_{2} \mathrm{O}(g)$
c. $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}(l)+\mathrm{O}_{2}(g) \rightarrow$
$\quad \mathrm{CH}_{3} \mathrm{CHO}(a q)+\mathrm{H}_{2} \mathrm{O}(l)$
d. $\mathrm{Fe}_{2} \mathrm{O}_{3}(s)+\mathrm{Al}(s) \rightarrow \mathrm{Fe}(l)+\mathrm{Al}_{2} \mathrm{O}_{3}(s)$

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