The formation reaction of magnesium oxide is as follows:

Mg (s) + 0.5O2 (g) → MgO (s)

This reaction can be constructed from the following reactions.

In the blanks before each reaction, add a coefficient that shows how they must be scaled before being added to give the reaction above. If the reversal of a reaction is required, indicate this using a negative sign before the coefficient. For example, if a reaction must be multiplied by 2 and reversed, write "-2."

(a) ___ Mg (s) + 2HCl (aq) → Mg2 + (aq) + 2Cl - (aq) + H2 (g)

(b) ___ MgO (s) + 2HCl (aq) → Mg2 + (aq) + 2Cl - (aq) + H2O (l)

(c) ___ H2 (g) + 0.5O2 (g) → H2O (l)

(a) 1

(b) - 1

(c) 1

Explanation:

In this type of questions use the strategy to look for placing the products and reactants on their right side.

For b) we notice MgO is a product in our reaction, therefore reverse the equation, the coefficient is 1 since there is one mol MgO product

Mg2 + (aq) + 2Cl - (aq) + H2O (l) → MgO (s) + 2HCl (aq)

We can notice that HCl is not a product in our final reaction, so we want to cancel it. If we add (a) to the one above, we get:

Mg (s) + 2HCl (aq) → Mg2 + (aq) + 2Cl - (aq) + H2 (g)

+

Mg2 + (aq) + 2Cl - (aq) + H2O (l) → MgO (s) + 2HCl (aq)

Mg (s) + H2O (l) → H2 (g) + MgO (s)

Finally adding this last equation to (c) we get our sought equation:

Mg (s) + H2O (l) → H2 (g) + MgO (s)

+

H2 (g) + 0.5O2 (g) H2O (l)

Mg (s) + 0.5O2 (g) → MgO (s)

So we only needed to reverse the sign for the first equation, and our answer should be

(a) 1

(b) - 1

(c) 1