Chemical change

Question 1

What is the law of conservation of mass?

Answer 1

Atoms are not created or destroyed in a chemical reaction

Question 2

In the reaction carbon + oxygen  carbon dioxide, why does the mass decrease?

Answer 2

Atoms are being lost as a gas (carbon dioxide)

Question 3

In the reaction magnesium + oxygen  magnesium oxide, why does the mass increase?

Answer 3

Atoms from a gas (oxygen) are being added

Question 4

What is a symbol equation?

Answer 4

A chemical equation in which the chemicals are represented by formulae

Question 5

What is a balanced equation?

Answer 5

A symbol equation where all the reactant atoms have become product atoms

Question 6

What do “big numbers” in front of formulae tell us?

Answer 6

How many units of each formula there is in the balanced equation

Question 7

Which numbers can be changed when balancing an equation?

Answer 7

Big numbers in front of formulae

Question 8

How can you tell if an equation is balanced?

Answer 8

Equal numbers of atoms of each element on each side of the reaction arrow

Question 9

Unit and symbol for mass?

Answer 9

Kilogram/kg (gram/g)

Question 10

Unit and symbol for volume?

Answer 10

Cubic metres/m3 (cubic centimetres/cm3) (cubic decimetre/dm3)

Question 11

What is concentration?

Answer 11

The amount of solute dissolved per unit volume of solvent

Question 12

Unit and symbol for concentration (when using mass)?

Answer 12

Grams per cubic decimetre – g/dm3

Question 13

What must particles do in order to have a chance to react?

Answer 13

Collide (with sufficient energy and in the correct orientation)

Question 14

What is rate of reaction?

Answer 14

How quickly a reaction takes place

Question 15

Units and symbols for rate?

Answer 15

Cubic centimetres per second (cm3/s) & grams per second (g/s)

Question 16

How can you monitor rate of reaction?

Answer 16

How quickly a product is formed or a reactant is used

Question 17

How can you measure how quickly a product is formed?

Answer 17

Volume of gas per second using a gas syringe, change in mass

Question 18

How can you measure how quickly a reactant is used?

Answer 18

Change in mass

Question 19

What is turbidity?

Answer 19

Cloudiness

Question 20

How can you monitor changes in concentration to measure rate?

Answer 20

Changes in colour or turbidity (disappearing cross)

Question 21

How can you calculate relative rate from time taken?

Answer 21

relative rate = 1/time taken

Question 22

On a graph of concentration/mass/volume of gas against time, what is represented by the gradient?

Answer 22

rate of reaction

Question 23

What are the 5 factors that can alter the rate of reaction?

Answer 23

Temperature, surface area, pressure (gases), concentration and catalyst

Question 24

How does temperature affect rate of reaction?

Answer 24

Increasing temperature increases rate of reaction

Question 25

What needs to happen to collisions between particles to increase rate?

Answer 25

Increased frequency and/or increased energy

Question 26

How do particles behave at higher temperatures?

Answer 26

They move faster and collide more frequently

Question 27

What do particles have more of at higher temperatures?

Answer 27

Energy

Question 28

Which state of matter can we alter the pressure of?

Answer 28

Gases

Question 29

How does pressure affect rate of reaction?

Answer 29

Increasing pressure increases rate of reaction

Question 30

How are particles spaced at high pressure?

Answer 30

Closer together – more particles per unit volume.

Question 31

How does concentration affect rate of reaction?

Answer 31

Increasing concentration increases rate of reaction

Question 32

How are particles spaced at low concentration?

Answer 32

Further apart – fewer particles per unit volume.

Question 33

What effect does breaking solid matter into smaller bits have on surface area?

Answer 33

Increases surface area to volume ratio.

Question 34

How does surface area affect rate of reaction?

Answer 34

Increasing surface area increases rate of reaction

Question 35

Why does a larger surface area increase rate of reaction?

Answer 35

More particles at the surface and available for collisions

Question 36

What is activation energy?

Answer 36

The minimum energy with which particles must collide in order to react

Question 37

What is a catalyst?

Answer 37

A chemical that increases the rate of a reaction without being used up itself

Question 38

How do catalysts increase the rate of reaction?

Answer 38

By decreasing the activation energy