Chemical Reactions

Question 1

What is a physical change?

Answer 1

a change that does not make a new substance and is often reversible (just changes state, size or shape)

Question 2

What is a chemical change

Answer 2

a change that creates a new substance and is often irreversible (Reactant atoms are rearranged to form a new product)

Question 3

What are some examples of a physical change?

Answer 3

ice melting, shredding paper, breaking a glass bottle, crumpling up a piece of foil

Question 4

What are some examples of a chemical change?

Answer 4

cooking a raw egg, baking bread, rust forming on an iron nail, burning wood

Question 5

What are some ways to identify if a chemical change has occurred?

Answer 5

formation of a gas, colour change, temperature change, energy emitted , production of a new odour/smell

Question 6

What is combustion?

Answer 6

commonly known as burning

Question 7

What are the 3 things needed for a combustion reaction?

Answer 7

oxygen, fuel (hydrocarbon) and heat (triangle)

Question 8

Combustion equation:

Answer 8

fuel + oxygen –> carbon dioxide + water

Question 9

Name some examples of fuels:

Answer 9

wood, oil , natural gas, coal , hydrogen

Question 10

What is very fast combustion?

Answer 10

An explosion

Question 11

What is respiration?

Answer 11

a chemical reaction in the body cells to release energy

Question 12

What is aerobic respiration?

Answer 12

respiration with oxygen ; glucose + oxygen
–> carbon dioxide + water

Question 13

Where does aerobic respiration take place?

Answer 13

mitochondria

Question 14

What is ATP?

Answer 14

an energy molecule that is made during aerobic respiration releasing chemical energy from sugar

Question 15

What is anaerobic respiration?

Answer 15

respiration without oxygen (used when doing intensive exercises) ; glucose (in water) –> ethanol + carbon dioxide (+ energy) e.g. fermentation to make alcohol and bread

Question 16

Describe conservation of mass:

Answer 16

when mass is never lost or gained in a chemical reaction or a physical change as long as the products are not allowed to escape; atoms are just rearranged as no atoms are destroyed or created

Question 17

What is rusting?

Answer 17

rusting (chemical change) is the corrosion of iron. other metals corrode in a similar way but rusting is specific to iron ( it is orange and is an example of an oxidisation reaction)

Question 18

What are 2 things needed for rusting?

Answer 18

Oxygen and water

Question 19

The word equation for rusting?

Answer 19

Iron+ oxygen + water –> (hydrated) iron oxide

Question 20

List some preventions of rust:

Answer 20

-painting over metal
-adding oil or grease
-galvanising (zinc protecting iron)

Question 21

Another name for water:

Answer 21

dihydrogen monoxide

Question 22

What are the 3 rules for balancing equations?

Answer 22

-you cannot change the subscript numbers
-balance equations must be in pencil
-coefficients have to be whole numbers

Question 23

Steps for balancing an equation:

Answer 23

1) count atoms of each element on both sides
2) look where they do not match
3) find lowest common multiple
4) add coefficients in front of the chemicals (have to be whole numbers)