Answer:
17. Yes, it represents a chemical reaction. This is because new substances were formed from the original substance.
18. (a) Formation of new substances
(b) Evolution or absorption of large quantity of heat
(c)Change in mass of substances
Explanation:
17. In the model above, molecules of a compound of carbon and hydrogen (molecular formula is C2H6) combines with molecular oxygen (O2) to produce two new substances; a compound composed of two oxygen atoms and one carbon atom (CO2) and another compound composed of two atoms of hydrogen and one atom of oxygen (H2O). Since the new substances formed are completely different from the original substances, it a chemical reaction. Also, a large volume of heat would have been given off.
18. To determine if a chemical reaction has occurred, the following observations can be looked out for.
a. Formation of new substances different entirely from the original substances
b. Evolution or absorption of large quantity of heat during the change. Check whether the vessel containing the substances gets hotter or colder.
c. Change in mass of substances. Since new substances are formed in a chemical reaction, there is usually a significant change in mass of the products and reactants.
