2.       a.       2 Mg_(s)          +           O_2(g)         2 MgO_(s)

Two moles of solid magnesium react with one mole of oxygen gas to produce 2 moles of solid magnesium oxide.

b.       2 H_2(g) +        O_2(g)         2 H₂O_(l)

Two moles of hydrogen gas react with one mole of oxygen gas to produce 2 moles of liquid water.

c.       NaOH_(aq)      +        HCl_(aq)                H₂O_(l)     +     NaCl_(aq)

One mole of sodium hydroxide reacts with one mole of hydrochloric acid (stomach acid) to produce 1 mole  of liquid water and 1 mole of sodium chloride.

d.       2 Al_(s) +        Fe₂O_3(s)                       Al₂O_{3 (s)}       +        2 Fe_(l)

Two moles of solid aluminum react with one mole of  Fe₂O_3(s) (we’ll learn how to name this rust soon) to  produce 1 mole  of solid aluminum oxide and 2 moles of liquid iron.

e.       C_(s)     +        H₂O_(g)                           CO_(g)   +       H_2(g)

One mole of carbon reacts with one mole of gaseous water (steam) to produce 1 mole of carbon monoxide gas and 1 mole of hydrogen gas.

3.       In #2d, the iron is produced as a liquid. What does that tell you about the energy associated with the reaction?

The reaction releases a lot of heat. It is known as an exothermic reaction. If the opposite was true: if the reaction removed heat fro the environment, it would have been an endothermic reaction.