Question

Give a balanced molecular chemical equation to illustrate each of the following types of reactions. a. a synthesis (combination) reaction b. a precipitation reaction c. a double-displacement reaction d. an acid-base reaction e. an oxidation-reduction reaction f. a combustion reaction

Short answer

a. \(2H_2(g) + O_2(g) \rightarrow 2H_2O(l)\) b. \(BaCl_2(aq) + Na_2SO_4(aq) \rightarrow BaSO_4(s) + 2NaCl(aq)\) c. \(2KI(aq) + Pb(NO_3)_2(aq) \rightarrow 2KNO_3(aq) + PbI_2(s)\) d. \(HCl(aq) + NaOH(aq) \rightarrow NaCl(aq) + H_2O(l)\) e. \(Zn(s) + CuSO_4(aq) \rightarrow ZnSO_4(aq) + Cu(s)\) f. \(CH_4(g) + 2O_2(g) \rightarrow CO_2(g) + 2H_2O(l)\)

Step-by-step solution

a. Synthesis (Combination) Reaction

A synthesis reaction occurs when two or more simple substances combine to form a more complex substance. The general pattern for this type of reaction is: \(A + B \rightarrow AB\). Example: Formation of water from hydrogen and oxygen: \[2H_2(g) + O_2(g) \rightarrow 2H_2O(l)\]

b. Precipitation Reaction

A precipitation reaction occurs when two solutions containing soluble salts are mixed and an insoluble salt is formed. The general pattern for this type of reaction is: \(AB(aq) + CD(aq) \rightarrow AD(s) + CB(aq)\) or \(AD(s) + CB(aq)\) Example: Formation of a precipitate of barium sulfate (BaSO4) from a solution of barium chloride (BaCl2) and a solution of sodium sulfate (Na2SO4): \[BaCl_2(aq) + Na_2SO_4(aq) \rightarrow BaSO_4(s) + 2NaCl(aq)\]

c. Double-Displacement Reaction

A double-displacement reaction occurs when two compounds exchange parts with each other to form two new compounds. The general pattern for this type of reaction is: \(AB + CD \rightarrow AD + CB\). Example: Reaction between potassium iodide (KI) and lead(II) nitrate (Pb(NO3)₂: \[2KI(aq) + Pb(NO_3)_2(aq) \rightarrow 2KNO_3(aq) + PbI_2(s)\]

d. Acid-Base Reaction

An acid-base reaction occurs when an acid reacts with a base, resulting in the formation of water and a salt. The general pattern for this type of reaction is: \(HA + BOH \rightarrow BA + H_2O\). Example: Reaction between hydrochloric acid (HCl) and sodium hydroxide (NaOH): \[HCl(aq) + NaOH(aq) \rightarrow NaCl(aq) + H_2O(l)\]

e. Oxidation-Reduction (Redox) Reaction

An oxidation-reduction reaction involves the transfer of electrons between chemical species. One species will lose electrons (oxidation) while another species will gain electrons (reduction). Example: Reaction between zinc metal (Zn) and copper(II) sulfate (CuSO4) to form zinc sulfate (ZnSO4) and copper metal (Cu): \[Zn(s) + CuSO_4(aq) \rightarrow ZnSO_4(aq) + Cu(s)\]

f. Combustion Reaction

A combustion reaction occurs when a hydrocarbon or any other substance reacts with oxygen to produce heat and light energy along with the formation of carbon dioxide (CO2) and water (H2O). Example: Combustion of methane (CH4): \[CH_4(g) + 2O_2(g) \rightarrow CO_2(g) + 2H_2O(l)\]

Key concepts

Synthesis Reaction

Imagine you're building something from lego blocks. Putting single blocks together to make a new shape is essentially what happens in a synthesis reaction, but with atoms and molecules. This reaction type involves combining simple substances to create a more complex compound. For instance, the reaction of hydrogen and oxygen to form water is a classic example: \[2H_2(g) + O_2(g) \rightarrow 2H_2O(l)\].
Such reactions are pivotal in chemical manufacturing where basic chemicals are synthesized into products like plastics, pharmaceuticals, and dyes.

Precipitation Reaction

Have you ever watched a snow globe? When you shake it, 'snow' appears to fall within the liquid. A precipitation reaction is somewhat similar, but instead of fake snow, a solid is formed when two solutions are mixed. This solid is called a precipitate. For example, if you mix solutions of barium chloride and sodium sulfate, barium sulfate precipitates out:\[BaCl_2(aq) + Na_2SO_4(aq) \rightarrow BaSO_4(s) + 2NaCl(aq)\].
This process helps to purify compounds in water treatment plants and to identify the presence of certain ions in a chemistry lab.

Double-Displacement Reaction

Think of this as a dance where two couples switch partners. In double-displacement reactions, two compounds swap components with each other, forming two entirely new compounds. This can be seen in the reaction between potassium iodide and lead(II) nitrate, producing lead(II) iodide and potassium nitrate:\[2KI(aq) + Pb(NO_3)_2(aq) \rightarrow 2KNO_3(aq) + PbI_2(s)\].
These reactions are useful for introducing different properties or removing toxic substances from an environment, like switching lead ions out of a solution.

Acid-Base Reaction

When we add opposites together—like an acid and a base—these substances can neutralize each other. In an acid-base reaction, the result is often a salt and water. A classic example is the reaction of hydrochloric acid with sodium hydroxide to form sodium chloride (table salt) and water:\[HCl(aq) + NaOH(aq) \rightarrow NaCl(aq) + H_2O(l)\].
This type of reaction is not only fundamental in chemistry but also has practical uses like treating indigestion caused by excess stomach acid.

Oxidation-Reduction Reaction

Oxidation-reduction, or redox reactions, involve the give and take of electrons. One substance will lose electrons (oxidized) while another one gains them (reduced). For instance, zinc metal can be oxidized by copper(II) sulfate, which in turn is reduced to metallic copper:\[Zn(s) + CuSO_4(aq) \rightarrow ZnSO_4(aq) + Cu(s)\].
These interactions are intrinsic to processes like battery operation and metabolic reactions within our bodies.

Combustion Reaction

Combustion is what happens when you light a candle or a bonfire. It's a high-energy reaction where a fuel—typically a hydrocarbon—combines with oxygen to release energy in the form of light and heat. The by-products are usually carbon dioxide and water. Methane, a simple hydrocarbon, burns in the presence of oxygen to form these products: \[CH_4(g) + 2O_2(g) \rightarrow CO_2(g) + 2H_2O(l)\].
Understanding combustion is essential for improving the efficiency of engines and minimizing pollutants in automotive emissions.