Chemistry – Metals - Reactivity series | e-Consult

Potassium (K) reacts vigorously and exothermically with cold water. The reaction is very rapid and produces hydrogen gas and potassium hydroxide. The heat produced is often sufficient to ignite the hydrogen gas, leading to a small explosion. The reaction equation is:

Sodium (Na) also reacts vigorously with cold water, although less so than potassium. It produces hydrogen gas and sodium hydroxide. The reaction is exothermic, but the heat produced is usually not enough to ignite the hydrogen. The reaction equation is:

Calcium (Ca) reacts with cold water, but the reaction is much slower than that of sodium or potassium. It produces hydrogen gas and calcium hydroxide. The reaction is not exothermic and the hydrogen gas is not usually ignited. The reaction equation is:

The reactivity of these metals with water increases down the group (K > Na > Ca). This is because the ionization energy decreases down the group, making it easier to lose electrons and form the metal ion. The smaller ionic radius of potassium also contributes to the higher reactivity.