Use the following equations to answer the next five questions:
i. h2o --> h2o
ii. na+ + cl- ag+ + no3- --> agcl + na+ + no3-
iii. ch3oh + o2 --> co2 + h2o
iv. 2h2o --> 2h2 + o2
v. h+ + oh- --> h2o
(a) which equations describes a physical change?
(b) which equation identifies the reactants and products of a combustion reaction?
(c) which equation is not balanced?
(d) which is a net ionic equation?

(a) i

(b) iii

(c) iii

(d) v

Explanation:

(a) A physical change does not alter the identity of the substance. Here the water remains water, but may change undergo a physical change such as vaporization or freezing.

(b) A combustion reaction usually involves the exothermic reaction of oxygen with another molecule to form carbon dioxide and water

(c) The reaction may be balanced as follows: CH₃OH + 3/2O₂ ⇒ CO₂ + 2H₂O

(d) A net ionic equation only takes into account the species that underwent a chemical change. Equation ii. for example, is not a net ionic equation because the Na⁺ and NO₃⁻ did not change in any way.