C3.1- Introducing Chemical Reactions

Question 1

Why are the formulae for metal elements written as the empirical formula?

Answer 1

Because metals exist as giant metallic lattices.

Question 2

Why don’t you include numbers when writing formulas for metal elements

Answer 2

• the numbers would be huge and would vary depending on the amount of metal

Question 3

Non metal elements in group 0…

Answer 3

Exist as individual atoms attracted to each other by weak intermolecular forces
-their formulae are the same as their chemical symbols

Question 4

Non metal elements in group 7…

Answer 4

Exist as diatomic molecules attracted to each other by weak intermolecular forces.
- the formula for group 7 elements all have a subscript 2

Question 5

Other non- metal elements exist as…

Answer 5

Giant covalent structures or as simple molecules

Question 6

The molecular formula for a simple covalent compound shows…

Answer 6

• the symbols for each element

- the number of atoms in each one of its molecules

Question 7

What is the law of conservation of mass?

Answer 7

Atoms cannot be created or destroyed by chemical reactions.

The same atoms are present at the start and end of a reaction.

The total mass stays the same during a chemical reaction.

Question 8

What is a closed system?

Answer 8

Apparatus in which substances cannot enter or leave the reaction mixture during a reaction

Question 9

What is a compound ion?

Answer 9

An ion formed when a group of atoms loses or gains electrons

Question 10

What is a diatomic molecule

Answer 10

They contain 2 atoms covalently bonded together

Question 11

What is a precipitate?

Answer 11

An insoluble product in the solid state formed during a reaction involving solutions

Question 12

What is a non-enclosed system?

Answer 12

Apparatus in which substances can enter or leave the reaction mixture during a reaction

• this usually happens in an open container when the reaction involves a substance in the gas state

Question 13

Why does the mass appear to go down in some reactions?

Answer 13

A gas is formed and escapes from the container so the mass appears to go down during the reaction

Question 14

What happens when a metal reacts with oxygen in the air?

Answer 14

The metal atoms combine with the oxygen atoms from the air to form a metal oxide in the solid state.

The mass appears to go up as you cannot measure the amount of oxygen used before the reaction

Question 15

What is a word equation.

Answer 15

a model of a reaction that describes reactants and products using their chemical names

Question 16

What is a balanced equation

Answer 16

a model for a reaction showing formulae and number of units for all substances involved. The numbers of each atom are the same on both sides of the equation

Question 17

What are state symbols

Answer 17

They show the physical state of each substance in a chemical reaction

Question 18

What is a half equation?

Answer 18

A half equation is a model for the change that happens to one reactant in a chemical reaction

Question 19

What is the half equation for sodium (Na)

Answer 19

Na —> Na+ + e-

Question 20

What is the half equation for chloride

Answer 20

Cl2 + 2e- —> 2Cl-

Question 21

What is an ionic equation

Answer 21

It shows the ions present in a reaction mixture

Question 22

What is a spectator ion?

Answer 22

It is in the reaction mixture but doesn’t take part in the reaction

Question 23

What is a mole?

Answer 23

It is the unit for amount of substance.
It is an amount of substance that contains the same number of particles (6.02 × 1023) as there are atoms in 12.0 g of 12C

Question 24

What is the Avogadro constant

Answer 24

It is the number of entities in one mol.

6.02 x 10^23

Question 25

How do you calculate the mass using moles

Answer 25

Mass (g) = molar mass (g/mol) x amount (moles)

Question 26

Calculating the number of moles

Answer 26

Moles = mass➗Mr

Question 27

What is stoichiometry

Answer 27

It describes the relative amounts of each substance involved in a chemical reaction