Write chemical equations for the following reactions:
(i) Calcium metal reacts with water.
(ii) Cinnabar is heated in the presence of air.
(iii) Manganese dioxide is heated with aluminium powder.
(b) What are alloys? List two properties of alloys.

Explanation

(i) `underset("Calcium")(Ca(s)) + underset("water")(2H_(2)O(l)) rarr underset("Clacium hydroxide")(Ca(OH)_(2)(aq))+ underset ("Hydrogen gas")(H_(2)(g))`
(ii) `underset ("Cinnabar")(2HgS(s))+ underset("from air") underset ("Oxygen") (3O_(2)(g)) overset("heat")(rarr) underset ("Cinnabar oxide") (2HgO(s)) + underset ("dioxide") underset("Sulphur") (2SO_(2)(g)`
(iii) `underset("dioxide")underset ("Manganese") (3MnO_(2)(s)) + underset("Aluminium") (4Al(s)) rarr underset("metal") underset("Manganses")(3Mn(l))+ underset ("oxide") underset ("Aluminium") (2Al_(2)O_(3)(s))+ Heat`
(b) Alloys are homogeneous mixtures of two or more metals of a metal and a non-metal
The properties of an alloy are different from the properties of the constituent metals.
In general-
`*` alloys are stronger than the metals from which they are made.
`*`alloys are mor resistant to corrosion.