Question

Assuming that each single-replacement reaction occurs, predict the products and write each balanced chemical equation. a) \(\mathrm{Mg}+\mathrm{HCl} \rightarrow ?\) b) \(\mathrm{HI}+\mathrm{Br}_{2} \rightarrow\) ?

Short answer

a) \( \mathrm{Mg} + 2\mathrm{HCl} \rightarrow \mathrm{MgCl}_2 + \mathrm{H}_2 \); b) \( 2\mathrm{HI} + \mathrm{Br}_2 \rightarrow 2\mathrm{HBr} + \mathrm{I}_2 \).

Step-by-step solution

Identify Reactants and Type of Reaction (a)

In the reaction \( \mathrm{Mg} + \mathrm{HCl} \rightarrow ? \), the reactants are magnesium (\( \mathrm{Mg} \)) and hydrochloric acid (\( \mathrm{HCl} \)). This is a single-replacement reaction where a metal replaces the hydrogen in the acid.

Predict Products of Reaction (a)

In a single-replacement reaction involving \( \mathrm{Mg} \) and \( \mathrm{HCl} \), magnesium replaces the hydrogen in hydrochloric acid. This results in the formation of magnesium chloride \( (\mathrm{MgCl}_2) \) and hydrogen gas \( (\mathrm{H}_2) \). Thus, the products are \( \mathrm{MgCl}_2 + \mathrm{H}_2 \).

Balance the Equation (a)

Start with the unbalanced equation: \( \mathrm{Mg} + \mathrm{HCl} \rightarrow \mathrm{MgCl}_2 + \mathrm{H}_2 \). To balance it, note that there are 2 chlorine atoms and 2 hydrogen atoms in the products, requiring 2 molecules of \( \mathrm{HCl} \) on the reactant side: \( \mathrm{Mg} + 2\mathrm{HCl} \rightarrow \mathrm{MgCl}_2 + \mathrm{H}_2 \).

Identify Reactants and Type of Reaction (b)

In the reaction \( \mathrm{HI} + \mathrm{Br}_2 \rightarrow ? \), the reactants are hydrogen iodide (\( \mathrm{HI} \)) and bromine (\( \mathrm{Br}_2 \)). This is also a single-replacement reaction where a halogen replaces another halogen in a compound.

Predict Products of Reaction (b)

During the reaction, bromine replaces the iodine in hydrogen iodide, leading to the formation of hydrogen bromide (\( \mathrm{HBr} \)) and iodine (\( \mathrm{I}_2 \)). Thus, the products are \( \mathrm{HBr} \) and \( \mathrm{I}_2 \).

Balance the Equation (b)

Start with the unbalanced equation: \( \mathrm{HI} + \mathrm{Br}_2 \rightarrow \mathrm{HBr} + \mathrm{I}_2 \). Notice that there are two iodines on the product side, so balance the iodine by having 2 molecules of \( \mathrm{HI} \) on the reactant side: \( 2\mathrm{HI} + \mathrm{Br}_2 \rightarrow 2\mathrm{HBr} + \mathrm{I}_2 \).

Key concepts

Chemical Equations

Chemical equations are symbolic representations of chemical reactions. They show the substances involved as well as their changes during the reaction. A typical chemical equation includes reactants, which are the starting substances on the left side, and products, which are the substances formed on the right side. Consider a simple equation for a single-replacement reaction such as \( \mathrm{Mg} + \mathrm{HCl} \rightarrow \mathrm{MgCl}_2 + \mathrm{H}_2 \). Here, magnesium (\( \mathrm{Mg} \)) and hydrochloric acid (\( \mathrm{HCl} \)) are reactants, while magnesium chloride (\( \mathrm{MgCl}_2 \)) and hydrogen gas (\( \mathrm{H}_2 \)) are the products.

When writing chemical equations, paying attention to the chemical formulas is essential. Your equations should accurately reflect the substances involved. It's also important to understand the state of each substance, such as whether it's in solid, liquid, or gaseous form. This helps in visualizing the reaction dynamics.

Balancing Reactions

Balancing reactions is the process of ensuring that a chemical equation obeys the law of conservation of mass. This law states that mass cannot be created or destroyed in a chemical reaction. To balance an equation, the number of atoms of each element must be equal on both sides of the equation.

• Step 1: Write the unbalanced equation with the correct chemical formulas.
• Step 2: Tally the number of atoms of each element on both sides.
• Step 3: Adjust coefficients (the numbers before molecules) to make the number of atoms equal.

For example, the unbalanced equation \( \mathrm{Mg} + \mathrm{HCl} \rightarrow \mathrm{MgCl}_2 + \mathrm{H}_2 \) requires balancing. We see two chlorines and two hydrogens on the product side, which means we must have two molecules of \( \mathrm{HCl} \) on the reactant side, resulting in \( \mathrm{Mg} + 2\mathrm{HCl} \rightarrow \mathrm{MgCl}_2 + \mathrm{H}_2 \). Balancing allows us to accurately describe a chemical process and see how much of each substance is consumed or produced.

Reaction Prediction

Predicting the products of a reaction involves understanding the type of reaction and the behavior of the reactants. Single-replacement reactions, for example, involve one element replacing another in a compound. How do you predict this? Firstly, make sure that the element doing the replacing is more reactive than the one being replaced.

Consider the reaction \( \mathrm{Mg} + \mathrm{HCl} \rightarrow \)? Magnesium, a metal, replaces the hydrogen in the hydrochloric acid, producing magnesium chloride and hydrogen gas. Similarly, the reaction \( \mathrm{HI} + \mathrm{Br}_2 \rightarrow \)? In this case, bromine (\( \mathrm{Br}_2 \)) replaces iodine in hydrogen iodide, forming hydrogen bromide and iodine. Understanding the reactivity series and halogen reactivity trends helps in predicting which single-replacement reactions will occur.

Single-replacement reactions give us insight into the relative reactivity of metals and halogens. Whether predicting reactions in a lab or solving textbook exercises, these basic principles guide us in understanding chemical behavior.