Question

Predict the type of reaction (if any) that occurs between each pair of substances. Write balanced molecular equations for each. If no reaction occurs, write NO REACTION. (a) aqueous hydrochloric acid and aqueous copper(II) nitrate (b) liquid pentanol \(\left(\mathrm{C}_{5} \mathrm{H}_{12} \mathrm{O}\right)\) and gaseous oxygen (c) aqueous ammonium chloride and aqueous calcium hydroxide (d) aqueous strontium sulfide and aqueous copper(II) sulfate

Short answer

a) NO REACTION. b) C5H12O + 8O2 --> 5CO2 + 6H2O. c) 2NH4Cl + Ca(OH)2 --> 2NH3 + 2H2O + CaCl2. d) SrS + CuSO4 --> CuS(s) + SrSO4(s).

Step-by-step solution

Identify the type of reaction for (a)

For the reaction between aqueous hydrochloric acid (HCl) and aqueous copper(II) nitrate (Cu(NO3)2), we look for possible exchange of ions that could result in the formation of a precipitate, a gas, or water. Both reactants are soluble, but no precipitate, gas, or water formation is evident. Therefore, there is no reaction.

Write the balanced molecular equation for (a)

Since no reaction occurs, we simply state: NO REACTION.

Identify the type of reaction for (b)

The reaction between liquid pentanol (C5H12O) and gaseous oxygen (O2) is a combustion reaction. In a combustion reaction, an organic compound reacts with oxygen to produce carbon dioxide (CO2) and water (H2O).

Write the balanced molecular equation for (b)

The balanced equation for the combustion of pentanol is: C5H12O + 8O2 --> 5CO2 + 6H2O.

Identify the type of reaction for (c)

The reaction between aqueous ammonium chloride (NH4Cl) and aqueous calcium hydroxide (Ca(OH)2) is a double displacement reaction, which can result in the formation of a precipitate. In this case, the expected products are calcium chloride (CaCl2) and ammonia (NH3) with water (H2O).

Write the balanced molecular equation for (c)

The balanced equation for this double displacement reaction is: 2NH4Cl + Ca(OH)2 --> 2NH3 + 2H2O + CaCl2.

Identify the type of reaction for (d)

The reaction between aqueous strontium sulfide (SrS) and aqueous copper(II) sulfate (CuSO4) is another double displacement reaction. We look for formation of a precipitate or another indicative sign of a chemical reaction.

Write the balanced molecular equation for (d)

The balanced equation with the exchange of ions between strontium sulfide and copper(II) sulfate result in the formation of copper(II) sulfide (CuS), which is a precipitate, and aqueous strontium sulfate (SrSO4), which is also a precipitate: SrS + CuSO4 --> CuS(s) + SrSO4(s).

Key concepts

Double Displacement Reaction

In a double displacement reaction, two compounds switch partners to form two new compounds. These reactions often occur in aqueous solutions and can produce precipitates, gases, or water. Let's look at one example mentioned in our exercise: when aqueous ammonium chloride reacts with aqueous calcium hydroxide, it's a swap between the cations and anions.
By understanding solubility rules and reactivity series, predicting the products of such reactions becomes easier. Remember, if no solid, gas, or molecular compound forms, then no visible reaction has occurred, as in the pairing of hydrochloric acid and aqueous copper(II) nitrate.

Combustion Reaction

Combustion reactions are energetic and result in fire or explosion if they happen rapidly. These involve oxygen and typically produce carbon dioxide and water. This type of reaction is exothermic, releasing heat, sometimes light. An example from our exercise is the combustion of pentanol, a type of alcohol. Through balancing the equation, the stoichiometry allows us to see the required amounts of oxygen needed to ensure complete combustion, which is critical for avoiding the production of harmful incomplete combustion products like carbon monoxide or soot.

Predicting Chemical Reactions

Predicting whether a chemical reaction will occur and its products is a fundamental skill in chemistry, useful both in industry and in understanding environmental processes. Through knowledge of reactivity, solubility, and energy considerations, chemists suggest possible outcomes when different substances are mixed. While not all potential reactions are straightforward to predict, known patterns such as those in double displacement and combustion reactions provide valuable guidance. If no reaction is predicted, like in the non-reactive mixture of hydrochloric acid with copper(II) nitrate, we deem it as such.

Writing Balanced Molecular Equations

When we write balanced molecular equations, we ensure the conservation of mass by having the same number of each type of atom on both sides of the equation. Steps involve identifying the reactants and products, balancing one element at a time, and adjusting coefficients to get the same amount of atoms of each element on both sides. As in our exercises, balanced equations give insight into the proportions of reactants needed, the amount of products formed, and they form the basis for further calculations in stoichiometry.