What is an example of single replacement reaction?

Tarnish is a chemical reaction that occurs whenever silver metal combines with hydrogen sulfide gas produced by various industrial operations or as a consequence of rotting animal or plant elements, as demonstrated in the spoon here.

A variety of polishes may be used to remove the tarnish, but the technique also loses a little bit of silver in the process. What is of interest, is the type of reaction that is taking place. Silver removes hydrogen from the sulfide and forms silver sulfide. This type of reaction is also known as a single replacement reaction.

REPLACEMENT REACTION

• When elements in a compound swap locations, this is called a replacement reaction. Ions (electrically charged counterparts of atoms) or ionic compounds are involved in this sort of reaction.
• In most cases, a more reactive component substitutes a less reactive element, and the less reactive component is liberated from the combination.

SINGLE REPLACEMENT REACTION

• A single replacement reaction happens whenever one element replaces the other in a single component. The general expression for this sort of reaction is:

  A + BC → B + AC

• When potassium combines with water, it is an example of a single substitution reaction. Potassium hydroxide, a white solid chemical, is formed, and hydrogen gas is released.

  2K + 2H₂O → 2KOH + H₂

• According to the expression, a potassium ion substitutes one of the hydrogen atoms within every water molecule in this process. Because potassium is a powerful oxidizing group 1 alkali metal, it reacts violently with water.

HYDROGEN REPLACEMENT REACTION

Many metals readily react with acids, and one of the results of the process is hydrogen gas. Aqueous zinc chloride and hydrogen are formed when zinc combines with hydrochloric acid.

The hydrogen in the acid is substituted by an active metal in a hydrogen replacement process.

PREDICTING IF A SINGLE REPLACEMENT REACTION WILL OCCUR

For specific types of reactions, such as single replacement reactions, the reactivity series—also known as the activity series—ranks constituents in a sequence of their reactivity. In the reactivity series, the more reactive components will displace the less reactive elements, but the other way around is not possible.

CONCLUSION:

• A single replacement reaction happens whenever one element replaces the other in a single component.
• Many metals readily react with acids, and one of the results of the process is hydrogen gas.
• Aqueous zinc chloride and hydrogen are formed when zinc combines with hydrochloric acid.

FAQs:

1. Is Zn + 2HCl = ZnCl₂ + H₂ a single replacement reaction?

Yes, zinc reacting with hydrochloric acid giving zinc chloride and hydrogen gas as products, is a typical example of a single replacement reaction.

2. What happens when Zn reacts with HCl?

When zinc reacts with HCl, zinc displaces hydrogen from hydrochloric acid and form zinc chloride. Hydrogen gas is released as a by-product.

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A single-replacement reaction, also called a single-displacement reaction, is a reaction in which one element is substituted for another element in a compound. In order to understand the chemistry of a single-replacement reaction, one has to know about the activity series of elements in the periodic table. Elements that are higher in the series have a greater tendency to gain or lose electrons and hence, can easily displace elements that are lower in the series. Both metals and nonmetals participate in replacement reactions [1-5].

General Equation for Single-replacement Reaction

The single-displacement reaction equation is:

A + BC → AC + B

This reaction will proceed if A is more reactive than B. When writing an actual reaction, the reaction must be balanced [1].

A characteristic of a single-replacement reaction is that one cation or anion trades places with another to form a new product. Metals that are more reactive than hydrogen readily dissolve in water. They form hydroxides and release hydrogen gas.

Examples of Single-replacement Reaction

An example of a single-displacement reaction occurs when potassium (K) reacts with water (H2O). A colorless solid compound named potassium hydroxide (KOH) forms, and hydrogen gas (H2) is set free. The equation for the reaction is:

2 K (s) + 2 H2O (l) → 2 KOH + H2 (g)

Consider the following example. Magnesium (Mg) replaces hydrogen (H) in hydrochloric acid (HCl) and forms magnesium chloride (MgCl2) and gaseous hydrogen (H2).

Mg (s) + HCl (aq.) → MgCl2 (s) + H2 (g)

This equation is not balanced. We note that there are two hydrogen and chlorine atoms on the right-hand side of the equation. So, we multiply the compound HCl on the left by 2 and balance the two atoms.

Mg (s) + 2 HCl (aq.) → MgCl2 (s) + H2 (g)

Rules for Prediction of Single-replacement Reaction

The periodic table or an activity series can help to predict whether single-replacement reactions occur. Whether one element will replace another element from a compound can be determined by the relative reactivities of the two elements. A single-replacement reaction will occur when a less reactive element can be replaced by a more reactive element in a compound [2].

1. Halogens

Order of reactivity of the halogens:

More reactive     F2  >  Cl2  >  Br2  >  I2    Less reactive

From this order, one can see that chlorine (Cl2) will replace bromine (Br2) from a bromide compound but cannot replace fluorine (F2) from a fluoride compound.

2. Metals

Order of reactivity of metals:

More reactive    Cu  >  Ag  >  Hg  >  Pt  >  Au    Less reactive

From this order, one can see that copper (Cu) will replace silver (Ag) in an aqueous solution consisting of Ag+ ions but not vice-versa.

Types of Single-replacement Reaction

There are two types of single-replacement reactions [2-4].

1. Cation Replacement

A cation is a positively charged ion or a metal. In this type of reaction, one cation replaces another.

Examples

• Zinc (Zn) can safely dissolve in hydrochloric acid (HCl), releasing hydrogen (H2) gas [1].

Zn (s) + 2 HCl (aq.) → ZnCl2 (s) + H2 (g)

• Copper (Cu) can displace silver (Ag) in an aqueous solution of silver nitrate (AgNO3).

Cu (s) + 2 AgNO3 (aq.) → Cu(NO3)2 (aq.) + 2 Ag (s/ppt.)

2. Anion Replacement

An anion is a negatively charged ion or a nonmetal. In this type of reaction, one anion replaces another.

Examples

• Chlorine (Cl2) will displace the bromine (Br2) in a sodium bromide (NaBr) compound because it is more reactive than bromine [1].

Cl2 (aq.) + 2 NaBr (aq.) → 2 NaCl (aq.) + Br2 (aq.)

• Bromine (Br2) replaces iodine (I2) in a reaction between bromine (Br2) and potassium iodide (KI).

Br2 (aq.) + 2 KI (aq.) → 2 KBr (aq.) + I2 (aq.)

Single-replacement Reactions Examples in Everyday Life

There are a few examples of single-replacement reactions taking place in nature and real life.

• The reaction of saltwater with concrete pillars containing iron forms iron (II) chloride
• Silver reacts with hydrogen sulfide gas that is produced by some industrial processes or as a result of decaying animal or plant materials. The reaction results in silver sulfide and hydrogen gas.

References