Question

Write a balanced chemical equation showing how each metal reacts with \(\mathrm{HBr}\). (a) \(\mathrm{Rb}\) (b) \(\mathrm{Mg}\) (c) \(\mathrm{Ba}\) (d) \(\mathrm{Al}\)

Short answer

Balanced chemical equations: (a) 2 Rb + 2 HBr → 2 RbBr + H2 (b) Mg + 2 HBr → MgBr2 + H2 (c) Ba + 2 HBr → BaBr2 + H2 (d) 2 Al + 6 HBr → 2 AlBr3 + 3 H2

Step-by-step solution

Writing out the Reaction for Rb with HBr

Identify the reactants which are Rb (rubidium) and HBr (hydrobromic acid). Rb is an alkali metal and HBr is an acid, so the reaction will produce a salt (rubidium bromide, RbBr) and hydrogen gas (H2). The unbalanced equation is: Rb(s) + HBr(aq) → RbBr(aq) + H2(g).

Balancing the Equation for Rb and HBr

Balance the number of atoms of each kind in the reactants and products. For Rb reacting with HBr, the balanced equation is: 2 Rb(s) + 2 HBr(aq) → 2 RbBr(aq) + H2(g), because two moles of Rb and HBr will produce one mole of hydrogen gas.

Writing out the Reaction for Mg with HBr

Identify the reactants which are Mg (magnesium) and HBr. The reaction will produce a salt (magnesium bromide, MgBr2) and hydrogen gas. The unbalanced equation is: Mg(s) + HBr(aq) → MgBr2(aq) + H2(g).

Balancing the Equation for Mg and HBr

Balance the atoms. For Mg reacting with HBr, the balanced equation is: Mg(s) + 2 HBr(aq) → MgBr2(aq) + H2(g). One mole of magnesium reacts with two moles of hydrobromic acid to produce one mole of hydrogen gas.

Writing out the Reaction for Ba with HBr

Identify the reactants which are Ba (barium) and HBr. This reaction will also yield a salt (barium bromide, BaBr2) and hydrogen gas. The unbalanced equation is: Ba(s) + HBr(aq) → BaBr2(aq) + H2(g).

Balancing the Equation for Ba and HBr

Balance the equation. The balanced equation for Ba reacting with HBr is: Ba(s) + 2 HBr(aq) → BaBr2(aq) + H2(g).

Writing out the Reaction for Al with HBr

Identify the reactants which are Al (aluminum) and HBr. This reaction will produce aluminum bromide (AlBr3) and hydrogen gas. The unbalanced equation is: Al(s) + HBr(aq) → AlBr3(aq) + H2(g).

Balancing the Equation for Al and HBr

Balance the equation. Since aluminum forms a tri-bromide, the balanced equation for Al reacting with HBr is: 2 Al(s) + 6 HBr(aq) → 2 AlBr3(aq) + 3 H2(g). This balances the aluminum, bromine, and hydrogen atoms on both sides of the equation.

Key concepts

Chemical Reactions

Chemical reactions are processes in which substances, known as reactants, transform into new substances called products.

During a reaction, the bonds between atoms in the reactants are broken, and new bonds form to create the products. This transformation is governed by certain laws, one being the law of conservation of mass, which states that mass cannot be created or destroyed in a chemical reaction. Thus, the mass of the reactants is equal to the mass of the products.

Types of Chemical Reactions

There are various types of chemical reactions, including combination, decomposition, single-replacement, double-replacement, and combustion reactions. The reactions in our exercise are examples of single-replacement reactions, which involve elements swapping places. For instance, rubidium (Rb) replaces the hydrogen (H) in hydrobromic acid (HBr) to form rubidium bromide (RbBr) and hydrogen gas (H2).

Stoichiometry

Stoichiometry is a branch of chemistry that deals with the quantitative relationships between reactants and products in a chemical reaction.

In stoichiometry, the coefficients in a balanced chemical equation represent the relative amounts of moles of each substance involved in the reaction. To balance an equation, you must ensure that the number of atoms for each element is the same on both sides of the equation, adhering to the principle of conservation of mass.

Steps in Balancing Equations

To balance a chemical equation, you typically start with the compound that contains the greatest number of different elements. Then, you use coefficients to balance the elements one at a time, adjusting the coefficients as necessary to achieve balance.

Compounds and Elements

Compounds and elements are two fundamental types of chemicals.

Elements are simple substances that cannot be broken down into simpler substances by chemical means. There are 118 elements known, each with its own unique properties, and they are the building blocks of all matter.

Compounds, on the other hand, are substances formed when two or more elements are chemically bonded together. The properties of a compound are different from the properties of the elements that comprise it. For example, rubidium bromide (RbBr), magnesium bromide (MgBr2), barium bromide (BaBr2), and aluminum bromide (AlBr3) in our exercise are all compounds formed from the reaction of an element with hydrobromic acid.

Reaction Prediction

Predicting chemical reactions involves determining what products will form when certain reactants are combined.

Chemists use the reactivity series of metals to predict the products of reactions involving metals and acids. A metal will displace another in a compound if it is higher in the series. In the case of our exercise, rubidium, magnesium, barium, and aluminum all react with hydrobromic acid to produce their respective bromides and hydrogen gas.

Reactivity Patterns

Understanding the periodic table and the properties of elements can also assist in predicting reactions. For example, alkali metals like rubidium react vigorously with acids, and as we move down the group in the periodic table, the metals tend to react more violently. Predicting reactions is an essential skill for chemists, as it allows the anticipation and control of chemical processes.