Question

Write balanced equations for each of the following reactions (some of these are analogous to reactions shown in the chapter). (a) Aluminum metal reacts with acids to form hydrogen gas. (b) Steam reacts with magnesium metal to give magnesium oxide and hydrogen. (c) Manganese(IV) oxide is reduced to manganese(II) oxide by hydrogen gas. (d) Calcium hydride reacts with water to generate hydrogen gas.

Short answer

The balanced equations for the given reactions are: (a) \(2Al + 6HCl \rightarrow 2AlCl_{3} + 3H_{2}\) (b) \(H_{2}O + Mg \rightarrow MgO + H_{2}\) (c) \(MnO_{2} + 2H_{2} \rightarrow MnO + 2H_{2}O\) (d) \(CaH_{2} + 2H_{2}O \rightarrow Ca(OH)_{2} + 2H_{2}\)

Step-by-step solution

Writing the unbalanced equation for the reaction involving Aluminum and an acid.

The general equation for the reaction of aluminum (Al) with an acid (HX) is: Al + HX → AlX + H_2 Here, X represents the anion from the acid. Since no specific acid is mentioned, we will choose a common acid for the example, such as hydrochloric acid (HCl).

Balancing the equation for Aluminum and hydrochloric acid reaction.

Now we balance the unbalanced equation: Al + HCl → AlCl_3 + H_2 Balancing the elements on both sides: 2Al + 6HCl → 2AlCl_3 + 3H_2 So the balanced equation is: \(2Al + 6HCl \rightarrow 2AlCl_{3} + 3H_{2}\) (b) Steam reacts with magnesium metal to give magnesium oxide and hydrogen.

Writing the unbalanced equation for the reaction involving steam and magnesium.

The given reaction can be written as: H_2O (steam) + Mg → MgO + H_2

Balancing the equation for the steam and magnesium reaction.

Now we balance the unbalanced equation: H_2O + Mg → MgO + H_2 Balancing the elements on both sides: H_2O + Mg → MgO + H_2 So the balanced equation is: \(H_{2}O + Mg \rightarrow MgO + H_{2}\) (c) Manganese(IV) oxide is reduced to manganese(II) oxide by hydrogen gas.

Writing the unbalanced equation for the reduction of manganese(IV) oxide.

The given reaction can be written as: MnO_2 + H_2 → MnO + H_2O

Balancing the equation for the reduction of manganese(IV) oxide.

Now we balance the unbalanced equation: MnO_2 + H_2 → MnO + H_2O Balancing the elements on both sides: MnO_2 + 2H_2 → MnO + 2H_2O So the balanced equation is: \(MnO_{2} + 2H_{2} \rightarrow MnO + 2H_{2}O\) (d) Calcium hydride reacts with water to generate hydrogen gas.

Writing the unbalanced equation for the reaction involving calcium hydride and water.

The given reaction can be written as: CaH_2 + H_2O → Ca(OH)_2 + H_2

Balancing the equation for the reaction between calcium hydride and water.

Now we balance the unbalanced equation: CaH_2 + H_2O → Ca(OH)_2 + H_2 Balancing the elements on both sides: CaH_2 + 2H_2O → Ca(OH)_2 + 2H_2 So the balanced equation is: \(CaH_{2} + 2H_{2}O \rightarrow Ca(OH)_{2} + 2H_{2}\)

Key concepts

Balancing Chemical Equations

Balancing chemical equations is an important skill in chemistry. It ensures that the same number of each type of atom appears on both sides of the equation, reflecting the conservation of mass. When balancing, identify the different elements in the reaction and count their atoms. Adjust the coefficients (the numbers before molecules) to get the same number of each kind of atom on both sides.

• Start by writing the unbalanced equation with reactants and products.
• Balance one element at a time, usually beginning with the element that appears in the most complex compounds.
• Adjust coefficients, not subscripts, to balance atoms. Never change subscripts as it changes the substance's identity.
• Recheck all elements to ensure they are balanced. Adjust accordingly.

The systematic approach helps maintain stoichiometric relationships, ensuring no atoms are created or destroyed in chemical reactions.

Redox Reactions

Redox reactions involve the transfer of electrons between substances, resulting in changes in oxidation states. In a redox reaction, one substance undergoes oxidation (loses electrons) while another undergoes reduction (gains electrons).

• Oxidation refers to the loss of electrons, often causing an increase in oxidation state.
• Reduction refers to the gain of electrons, resulting in a decrease in oxidation state.
• In redox reactions, the substance that donates electrons is called the reducing agent, while the substance that accepts them is the oxidizing agent.
• Redox processes are crucial in various fields, including metabolism, industrial chemistry, and energy production.

Understanding redox reactions helps in analyzing chemical processes like combustion and metal corrosion, where electron exchange plays a key role.

Acid-Metal Reactions

Acid-metal reactions are a type of chemical reaction where an acid reacts with a metal, often producing hydrogen gas and a salt. This type of reaction is a classic example of acid reactivity.

• When acids react with active metals such as aluminum or zinc, hydrogen gas ( H_2) is often released, and a salt specific to the metal and acid is formed.
• The general formula can be expressed as: Metal + Acid → Salt + Hydrogen Gas.
• These reactions are exothermic, meaning they release heat.
• They are also practical in real-world applications such as metal etching and galvanic cells.

Learning about acid-metal reactions is essential as it lays the foundation for understanding more complex chemical interactions and applications in everyday life.