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 as follows: a) \(2Al(s) + 6HCl(aq) \rightarrow 2AlCl₃(aq) + 3H₂(g)\) b) \(Mg(s) + H₂O(g) \rightarrow MgO(s) + H₂(g)\) c) \(MnO₂(s) + 2H₂(g) \rightarrow MnO(s) + 2H₂O(g)\) d) \(CaH₂(s) + 2H₂O(l) \rightarrow Ca(OH)₂(aq) + 2H₂(g)\)

Step-by-step solution

Write the unbalanced equation

Al(s) + HCl(aq) -> AlCl₃(aq) + H₂(g)

Balance the equation

To balance the equation, we need 6 HCl molecules to produce 3 H₂ molecules so that there are 6 H atoms on both sides of the equation. So, the balanced equation will be: 2Al(s) + 6HCl(aq) -> 2AlCl₃(aq) + 3H₂(g) #b)# Steam reacts with magnesium to give magnesium oxide and hydrogen

Write the unbalanced equation

Mg(s) + H₂O(g) -> MgO(s) + H₂(g)

Balance the equation

To balance the equation, we simply need 1 Mg atom, 1 H₂O molecule, 1 MgO molecule and 1 H₂ molecule, as there are already equal numbers of Mg, O and H atoms on both sides. The balanced equation is: Mg(s) + H₂O(g) -> MgO(s) + H₂(g) #c)# Manganese(IV) oxide is reduced to manganese(II) oxide by hydrogen gas

Write the unbalanced equation

MnO₂(s) + H₂(g) -> MnO(s) + H₂O(g)

Balance the equation

To balance this equation, 2 H atoms are needed on both sides of the equation. The balanced equation is: MnO₂(s) + 2H₂(g) -> MnO(s) + 2H₂O(g) #d)# Calcium hydride reacts with water to generate hydrogen gas

Write the unbalanced equation

CaH₂(s) + H₂O(l) -> Ca(OH)₂(aq) + H₂(g)

Balance the equation

In this case, we need the same number of H, Ca and O atoms on both sides of the equation: 2 H₂O molecules provide 4 H atoms to balance the 4 H atoms from CaH₂ and H₂. The balanced equation is: CaH₂(s) + 2H₂O(l) -> Ca(OH)₂(aq) + 2H₂(g)