Lithium metal and finely divided magnesium react with which substance?

Lithium metal and finely divided magnesium react with which substance?

• A. Oxygen
• B. Water
• C. Nitrogen
• D. Carbon dioxide

Answer: (B)

Lithium metal and finely divided magnesium react with water to form metal hydroxide and hydrogen gas, an exothermic process that can be hazardous. When lithium meets water, it undergoes 2 Li + 2 H2O → 2 LiOH + H2, releasing heat and hydrogen. Magnesium reacts with water to give Mg(OH)2 and H2 (Mg + 2 H2O → Mg(OH)2 + H2); with steam, the reaction is even more vigorous (Mg + H2O → MgO + H2). The other substances listed don’t produce this characteristic hydrogen-release reaction with these metals under normal conditions, so water is the substance they react with in this context.

Lithium metal and finely divided magnesium react with water to form metal hydroxide and hydrogen gas, an exothermic process that can be hazardous. When lithium meets water, it undergoes 2 Li + 2 H2O → 2 LiOH + H2, releasing heat and hydrogen. Magnesium reacts with water to give Mg(OH)2 and H2 (Mg + 2 H2O → Mg(OH)2 + H2); with steam, the reaction is even more vigorous (Mg + H2O → MgO + H2). The other substances listed don’t produce this characteristic hydrogen-release reaction with these metals under normal conditions, so water is the substance they react with in this context.