Balancing equations Transitional Reasoning Download PDF

Questions

1. 1.

   An automotive safety engineer evaluates a propellant reaction inside a vehicle airbag module, where solid sodium azide ($\text{NaN}_3$) reacts with iron(III) oxide ($\text{Fe}_2\text{O}_3$) to produce sodium oxide ($\text{Na}_2\text{O}$), elemental iron ($\text{Fe}$), and nitrogen gas ($\text{N}_2$). The unbalanced chemical equation is given as $\text{NaN}_3 + \text{Fe}_2\text{O}_3 \to \text{Na}_2\text{O} + \text{Fe} + \text{N}_2$. When the equation is balanced using the lowest whole-number coefficients, what is the ratio of the coefficient of $\text{N}_2$ to that of $\text{NaN}_3$, and what is the sum of all stoichiometric coefficients?

   • A) Ratio is 3/1; sum of all coefficients is 18
   • B) Ratio is 3/2; sum of all coefficients is 14
   • C) Ratio is 2/3; sum of all coefficients is 21
   • D) Ratio is 3/2; sum of all coefficients is 21
2. 2.

   A chemical process engineer oversees the hydrolysis of solid tetraphosphorus decasulfide ($\text{P}_4\text{S}_{10}$) with liquid water to produce aqueous phosphoric acid ($\text{H}_3\text{PO}_4$) and toxic hydrogen sulfide gas ($\text{H}_2\text{S}$). The unbalanced chemical equation for this conversion is $\text{P}_4\text{S}_{10}\text{(s)} + \text{H}_2\text{O(l)} \to \text{H}_3\text{PO}_4\text{(aq)} + \text{H}_2\text{S(g)}$. When the equation is balanced using the lowest whole-number coefficients, how many moles of water are required per mole of phosphoric acid produced, and what is the stoichiometric coefficient of hydrogen sulfide?

   • A) 4 moles of water; coefficient of hydrogen sulfide is 10
   • B) 16 moles of water; coefficient of hydrogen sulfide is 10
   • C) 4 moles of water; coefficient of hydrogen sulfide is 5
   • D) 2 moles of water; coefficient of hydrogen sulfide is 5
3. 3.

   A chemical technician in an electroplating facility treats metallic copper scrap with concentrated nitric acid to generate an aqueous copper(II) nitrate solution, releasing nitrogen dioxide gas and water vapor. The unbalanced chemical reaction is represented by $\text{Cu(s)} + \text{HNO}_3\text{(aq)} \to \text{Cu(NO}_3)_2\text{(aq)} + \text{NO}_2\text{(g)} + \text{H}_2\text{O(l)}$. To accurately size acid dosing pumps and exhaust scrubber units, the technician must balance the equation using the lowest whole-number coefficients. What is the stoichiometric coefficient of nitric acid, and what is the sum of the product coefficients in the balanced equation?

   • A) The coefficient of nitric acid is 4, and the sum of the product coefficients is 5.
   • B) The coefficient of nitric acid is 2, and the sum of the product coefficients is 4.
   • C) The coefficient of nitric acid is 4, and the sum of the product coefficients is 4.
   • D) The coefficient of nitric acid is 3, and the sum of the product coefficients is 6.
4. 4.

   A metallurgical engineer evaluates the roasting of iron pyrite, $FeS_2$, which reacts with oxygen gas, $O_2$, to produce solid iron(III) oxide, $Fe_2O_3$, and sulfur dioxide gas, $SO_2$. To size the gas intake and exhaust lines, the engineer balances the reaction equation using the lowest whole-number coefficients. What is the ratio of the stoichiometric coefficient of oxygen gas to that of sulfur dioxide, and what is the resulting coefficient of iron pyrite?

   • A) The ratio is 11:4, and the coefficient of $FeS_2$ is 2.
   • B) The ratio is 11:8, and the coefficient of $FeS_2$ is 4.
   • C) The ratio is 7:4, and the coefficient of $FeS_2$ is 2.
   • D) The ratio is 11:8, and the coefficient of $FeS_2$ is 2.
5. 5.

   An environmental chemist designs a treatment system to neutralize phosphine gas ($\text{PH}_3$) from industrial emissions by reacting it completely with oxygen gas ($\text{O}_2$) to produce solid diphosphorus pentoxide ($\text{P}_2\text{O}_5$) and water vapor ($\text{H}_2\text{O}$). To properly size the gas supply and analyze reactor stoichiometry, the reaction equation must be balanced. When this chemical equation is balanced using the lowest whole-number coefficients, which statement correctly identifies the coefficient of oxygen gas and the sum of all stoichiometric coefficients?

   • A) The coefficient of $\text{O}_2$ is 4, and the sum of all coefficients is 10.
   • B) The coefficient of $\text{O}_2$ is 4, and the sum of all coefficients is 9.
   • C) The coefficient of $\text{O}_2$ is 2, and the sum of all coefficients is 7.
   • D) The coefficient of $\text{O}_2$ is 8, and the sum of all coefficients is 20.