How many elements are involved in the reaction of calcium with water?

2 Answers
Jan 25, 2018

Three - Calcium (Ca), Hydrogen (H) and Oxygen (O).

Explanation:

Every element has it's own symbol. This symbol represents one atom of the given element. For example in your equation, Ca just means one atom of Calcium.

#H_2O# means you have two atoms of Hydrogen (H) and one atom of Oxygen (O).

The 2 before the #H_2O# means you have two lots of #H_2O# (i.e. four hydrogen atoms and two oxygen atoms).

A molecule is a combination of elements (bonded together), i.e. #H_2O# and #Ca(OH)_2#.

Therefore in your equation you have three elements present and three molecules present. (Ca itself is not a molecule here as it is not bonded to anything - unlike #H_2# which is as two hydrogen atoms are bonded together).

Jan 25, 2018

Are there not three elements in total...?

Explanation:

#Ca(s) + 2H_2O(l) rarr Ca(OH)_2(s)darr + H_2(g)uarr#

And the three elements are calcium metal, hydrogen as its oxide, and oxygen as its hydride....the calcium is oxidized and the hydrogen is reduced.