Chemistry Questions

2009-04-02 10:49 am

1. Is reactivity a physical property or a chemical property of metals?

2. Potasium(K) catches fire when put on water, why? It's due to what? Is that the reaction between K and water or reaction between K and
air?

回答 (1)

老爺子

2009-04-02 7:45 pm

✔ 最佳答案

1.
Reactivity of metal is a chemical property.
The term "reactivity" refers to the "reactivity of the metal in chemical reactions". Therefore, the term "reactivity" relates to the formation of new substances in chemical reactions.

2.
Potassium reacts with water vigorously:
2K(s) + 2H2O(l) → 2KOH(aq) + H2(g) ...ΔH = negative
Hydrogen is released and the reaction very exothermic. The heat given off will light up the hydrogen in air, i.e. to cause the reaction between hydrogen and oxygen.
2H2(g) + O2(g) → H2O(g) ...(burning of H2 in air)
A small amount of potassium ions (from KOH) in the flame gives a lilac flame (similar to the flame test of potassium compound).
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