Chemical equations Transitional Reasoning Practice

Questions

1. 1.

   A chemist investigates the reduction of black copper(II) oxide to metallic copper by passing dry ammonia gas over the heated solid according to the unbalanced equation: $\text{CuO}\text{(s)} + \text{NH}_3\text{(g)} \rightarrow \text{Cu}\text{(s)} + \text{N}_2\text{(g)} + \text{H}_2\text{O}\text{(g)}$. After balancing this equation with the lowest whole-number coefficients, which deduction accurately reflects the stoichiometric relationships and conservation principles shown?

   • A) The reaction conserves the total number of gas moles because two moles of gaseous reactant yield two moles of gaseous products.
   • B) The stoichiometric coefficient of water equals that of ammonia, maintaining a 1:1 mole ratio between them throughout the process.
   • C) For every 1 mole of diatomic nitrogen gas formed, exactly 2 moles of solid copper metal are precipitated.
   • D) Producing 1 mole of nitrogen gas requires the consumption of 3 moles of copper(II) oxide while simultaneously generating 3 moles of steam.
2. 2.

   A process engineer analyzes the Andrussow process for the industrial synthesis of hydrogen cyanide, represented by the balanced equation: $$2\text{CH}_4\text{(g)} + 2\text{NH}_3\text{(g)} + 3\text{O}_2\text{(g)} \rightarrow 2\text{HCN}\text{(g)} + 6\text{H}_2\text{O}\text{(g)}$$ To ensure proper operation of the reactor, the engineer must distinguish between quantities that are conserved and those that can change during the transformation. Which statement correctly interprets the stoichiometric relationships and conservation principles shown in this chemical equation?

   • A) The stoichiometric coefficients dictate that 2 grams of $\text{CH}_4$ react completely with 2 grams of $\text{NH}_3$ to yield 2 grams of $\text{HCN}$.
   • B) The reaction consumes 7 moles of gaseous reactant molecules to generate 8 moles of gaseous product molecules, confirming that total molecule count is not conserved even though atomic count is strictly conserved.
   • C) The reaction produces a greater total mass of products than reactants because the sum of the product coefficients (8) is greater than the sum of the reactant coefficients (7).
   • D) The reaction decreases the total volume of gas at constant temperature and pressure because the products contain a higher total number of atoms than the reactants.
3. 3.

   An environmental engineer examines a chemical scrubbing system that neutralizes gaseous chlorine dioxide emissions using aqueous sodium hydroxide according to the balanced equation: $2\text{ClO}_2\text{(g)} + 2\text{NaOH}\text{(aq)} \rightarrow \text{NaClO}_2\text{(aq)} + X\text{(aq)} + \text{H}_2\text{O}\text{(l)}$. Based on the law of conservation of atoms and the principles of chemical equations, which of the following correctly identifies compound $X$ and describes a valid conservation principle of this reaction?

   • A) Compound $X$ is $\text{NaClO}_3$, and the total number of atoms of each element is conserved while the total number of moles of gaseous substances decreases.
   • B) Compound $X$ is $\text{NaClO}_4$, and the total number of molecules must be conserved between the reactant and product sides of the equation.
   • C) Compound $X$ is $\text{NaCl}$, and the total number of moles of dissolved ions must equal the initial moles of gaseous reactants.
   • D) Compound $X$ is $\text{NaClO}_3$, and the total volume of all substances must be strictly conserved regardless of their physical states.
4. 4.

   An industrial chemist investigates the extraction of titanium metal through the Kroll process, in which gaseous titanium(IV) chloride reacts with molten magnesium according to the unbalanced equation: $\text{TiCl}_4\text{(g)} + \text{Mg}\text{(l)} \rightarrow \text{Ti}\text{(s)} + \text{MgCl}_2\text{(l)}$. When this chemical equation is balanced using the smallest set of whole-number coefficients, which of the following statements correctly describes the stoichiometric relationships and conservation principles of the reaction?

   • A) Consuming 1 mole of $\text{TiCl}_4$ requires 4 moles of $\text{Mg}$ and produces 4 moles of $\text{MgCl}_2$, conserving the number of chlorine atoms.
   • B) Consuming 1 mole of $\text{TiCl}_4$ requires 1 mole of $\text{Mg}$ because both metallic elements have a 1:1 stoichiometric coefficient in the balanced equation.
   • C) Consuming 1 mole of $\text{TiCl}_4$ requires 2 moles of $\text{Mg}$ and yields 2 moles of $\text{MgCl}_2$, conserving the total mass and the number of each type of atom.
   • D) Consuming 2 moles of $\text{TiCl}_4$ requires 1 mole of $\text{Mg}$ and yields 1 mole of $\text{MgCl}_2$, reflecting an inverse ratio between reactants and products.
5. 5.

   A chemical technician models the catalytic oxidation of ammonia in a closed reactor, represented by the unbalanced chemical equation: $\text{NH}_3\text{(g)} + \text{O}_2\text{(g)} \rightarrow \text{NO}\text{(g)} + \text{H}_2\text{O}\text{(g)}$. To optimize the feed rates, the equation must be balanced using the smallest set of whole-number coefficients. Which of the following correctly identifies the stoichiometric coefficient of oxygen gas and the mole ratio of water produced to ammonia consumed?

   • A) The coefficient of $\text{O}_2$ is 5, and the mole ratio of $\text{H}_2\text{O}$ to $\text{NH}_3$ is 3 : 2.
   • B) The coefficient of $\text{O}_2$ is 3, and the mole ratio of $\text{H}_2\text{O}$ to $\text{NH}_3$ is 1 : 1.
   • C) The coefficient of $\text{O}_2$ is 5, and the mole ratio of $\text{H}_2\text{O}$ to $\text{NH}_3$ is 2 : 3.
   • D) The coefficient of $\text{O}_2$ is 4, and the mole ratio of $\text{H}_2\text{O}$ to $\text{NH}_3$ is 3 : 2.

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