4 Write word equations for the following chemical reactions.
(a) Octane gas is burnt with oxygen in a car engine
to produce carbon dioxide and water.
(b) Sodium metal reacts with chlorine gas to form
sodium chloride.
(c) Hydrogen gas and oxygen gas combine to form
water.
(d) Zinc metal dissolves in hydrochloric acid to
form hydrogen gas and zinc chloride.

A) 2 C8H18 + 25 O2 → 16 CO2 + 18 H2O

B) 2Na + cl2 -> 2Nacl

C) 2H2+02 -> 2H20

D) Zn + 2Hcl -> Zncl2 + H2

answer : a model is often used to explain and make things easier to understand when any scientific topic needs to be demonstrated and explained.

as in this case where a scientist wants to use a model to present the results of his detailed scientific investigation. he should do it as it will him to make the audience understand the concept in a much better way. also, it can be changed according to new scientific understandings.