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Difficulty: EasyChemical Reactions and Compounds

Complete the statement and equation for the reaction between solid magnesium metal and hydrochloric acid. What coefficient balances the acid reactant, and what classification describes this reaction?

Answer:When solid magnesium reacts with aqueous hydrochloric acid, it forms dissolved magnesium chloride and hydrogen gas according to the equation: Mg+【2】HCl→MgCl2+H2\text{Mg} + 【2】\text{HCl} \rightarrow \text{MgCl}_2 + \text{H}_2. Because an uncombined element takes the place of another element in a compound, this process is classified as a 【single】 replacement reaction.

Answer

The balanced coefficient for HCl\text{HCl} is 22, and the reaction type is single replacement.
According to the Law of Conservation of Mass, matter is neither created nor destroyed during a chemical reaction. On the product side, MgCl2\text{MgCl}_2 contains two chlorine atoms and H2\text{H}_2 contains two hydrogen atoms. Therefore, a coefficient of 22 in front of HCl\text{HCl} is necessary to supply two hydrogen and two chlorine atoms from the reactants. Furthermore, because elemental magnesium displaces hydrogen from hydrochloric acid to yield magnesium chloride and free hydrogen, the reaction is by definition a single replacement (displacement) reaction.

Step-by-Step Solution

1
Count the atoms of each element on the product side of the equation
The products MgCl2+H2\text{MgCl}_2 + \text{H}_2 contain 11 magnesium atom, 22 chlorine atoms, and 22 hydrogen atoms.
The Law of Conservation of Mass requires the number of atoms of each element to be identical on both sides of a chemical equation.
2
Determine the coefficient needed for HCl\text{HCl} on the reactant side
Placing a coefficient of 22 in front of HCl\text{HCl} gives 22 hydrogen atoms and 22 chlorine atoms, balancing 1Mg+2HCl→1MgCl2+1H21\text{Mg} + 2\text{HCl} \rightarrow 1\text{MgCl}_2 + 1\text{H}_2.
Changing coefficients balances the total atom counts without altering chemical identities.
3
Classify the reaction mechanism based on reactant and product structures
The reaction is classified as a single replacement (or single displacement) reaction.
Free magnesium metal (Mg\text{Mg}) displaces hydrogen (H\text{H}) from hydrochloric acid (HCl\text{HCl}) to form a new compound and release elemental hydrogen gas.

Key Concept

Balancing chemical equations by conserving atoms and identifying single replacement reaction patterns.
Estimated Time:45s
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Topics

Chemical Reactions and Compounds

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