Chapter 11 (11.1) Identifying A Chemical Change

Question 1

Chemical change?

Answer 1

Change in which new substances (in the form of elements and/or compounds) are formed

Question 2

Physical change?

Answer 2

A change in which no new substances are formed

Question 3

What are the two groups chemical changes can be classified into?

Answer 3

1) Combination: reactants in which two or more substances chemically combine to form one or more new substances
2) Decomposition: reactions in which a substance breaks down into two or more new substances

Question 4

How to differentiate physical and chemical changes? (Differences)

Answer 4

Physical changes:
No new substances are formed
The changes can usually be reversed and we can get the constituents back using separation techniques
Chemical changes:
The changes are usually not easily reversed, we cannot get the reactants back easily

Question 5

What happens to energy during a chemical reaction?

Answer 5

It is sometimes taken in or given out (e.g. a large amount of heat is released when carbon burns/when calcium carbonate is heated)

Question 6

How to represent chemical reactions?

Answer 6

Use word equations (reactants used and products formed, sometimes it shows conditions)
E.g. methane+oxygen (reactants) -heat-> carbon dioxide+water (products)

Question 7

What happens to the total number of atoms before and after a chemical reaction?

Answer 7

The total number of atoms before and after a chemical reactions is balanced
(Number of each type of atom remains the same)

Question 8

What happens to the mass of the atoms during chemical reactions and why?

Answer 8

No atoms are lost and formed in a chemical reaction. Thus, the mass of the reactants is equal to the mass of the products and mass is conserved during a chemical reaction.