Moles

Question 1

What is relative mass

Answer 1

Mass cannot be measured using standard units (Too small)

Relative masses compare mass to 1/12 mass of Carbon-12 atom (No units)

Question 2

What is relative atomic mass

Answer 2

Relative mass of single atom (On periodic table)

Question 3

What is relative molecular mass

Answer 3

Relative mass of molecule (Sum of relative atomic masses of molecule)

Question 4

What is relative formula mass

Answer 4

Relative mass of formula unit of ionic / covalent network substance

Question 5

What is a mole

Answer 5

Measure number of atoms / molecules / formula units

Question 6

What is the value of 1 mole in particles

Answer 6

6.022 x 10^23 particles (Avogadro’s Number)

Amount of atoms in 12g of Carbon-12

Question 7

What is the formula for amount of substance in mole

Answer 7

Amount of substance in mole = (Amount of particles of substance) / (Number of particles in 1 mole)

Question 8

What is molar mass

Answer 8

Mass (g) of one mole of pure substance

Molar mass (g) = Relative mass (g)

Question 9

What is formula for molar mass

Answer 9

Amount of substance in mole = (Mass of substance) / (Molar mass of substance)

Question 10

What is percentage composition

Answer 10

Proportion by mass of different elements in compound

Question 11

What is formula for percentage composition

Answer 11

% by mass of element in compound = (Mass of element in 1 mole of compound) / (Molar mass of compound) * 100%

Question 12

What are chemical reactions

Answer 12

When particles collide, rearranged to form “new” substances

Question 13

What are energy changes in chemical reactions

Answer 13

Reactions involve breaking of chemical bonds, formation of new ones

• Breaking bonds require energy absorbed from surroundings
• Formation releases energy to surroundings
• Energy mostly heat, light, electricity (J, kJ, MJ)
• Change in chemical energy (Energy stored in chemical bonds) due to reaction

– Is converted to other forms

Question 14

What are phase changes either exothermic or endothermic

Answer 14

Liquid to gas = Endothermic, energy absorbed from surroundings

Liquid to solid = Exothermic, energy released to surroundings

Question 15

What is the conservation of energy

Answer 15

Energy cannot be created or destroyed, only transferred or transformed

System is chemical reaction, energy absorbed / released by system

• Absorbed / Released to surroundings (Eg. Air, Water, Container)

Question 16

What is exothermic reactions

Answer 16

Releases energy to surroundings

Question 17

What is properties of exothermic reactions

Answer 17

Chemical energy of products < reactants

Energy absorbed < Energy released

Lost energy released to surroundings

Feels warm (Temperature change to surroundings positive)

Question 18

What is endothermic reactions

Answer 18

Absorb energy from surroundings

Question 19

What is properties of endothermic reactions

Answer 19

Chemical energy of products > reactants

Energy absorbed > Energy released

Added energy absorbed to surroundings

Feels cold (Temperature change to surroundings negative)

Question 20

What are chemical equations of exothermic reactions

Answer 20

Energy added to products

Question 21

What are chemial equations of endothermic reactions

Answer 21

Energy added to reactants

Question 22

What is enthalpy

Answer 22

Stored chemical energy of substance (J), symbol H

Question 23

What is heat of change

Answer 23

Amount of energy absorbed / released in chemical reaction

Question 24

What is enthalpy change

Answer 24

Exchange of heat between system & surroundings

Enthalpy change = Enthalpy of products - Enthalpy of reactants

Question 25

What is enthalpy change in exothermic reactions

Answer 25

Negative

Question 26

What is enthalpy change in exothermic reactions

Answer 26

Positive

Question 27

What are enthalpy diagrams

Answer 27

Graphically show change in enthalpy as reaction proceeds

Question 28

What are bond enthalpies

Answer 28

Breaking bonds require energy = Endothermic process Forming bonds release energy = Exothermic process

Question 29

What is activation energy

Answer 29

Energy required to break bonds so chemical reaction can start

Question 30

What are energy profile diagrams

Answer 30

Show potential energy changes during course of chemical reaction

Question 31

How should energy profile diagrams in exothermic reactions look

Answer 31

Enthalpy of products < Enthalpy of reactants Overall energy is released

Question 32

How should energy profile diagrams in exothermic reactions look

Answer 32

Enthalpy of products > Enthalpy of reactants Overall energy is absorbed

Question 33

What are thermochemical equations

Answer 33

Sign and numerical value for energy change in equations Enthalpy change value for reaction quoted, accompanied by equation - Indicates amount, per mole, of energy released / absorbed

Question 34

What are exothermic reactions thermochemical equations

Answer 34

Enthalpy change negative Enthalpy change treated as reactant if written in equation

Question 35

What are endothermic reactions thermochemical equations

Answer 35

Enthalpy change positve Enthalpy change treated as product if written in equation

Question 36

What is the principle of energy changes per mole in thermochemical equations

Answer 36

Comparing enthalpy change, comparsions made "per mole" of reactants Chemical equation re-written - "Focus" reactant coefficient of 1

Question 37

What is the effect on enthalpy change when reversing chemical reaction

Answer 37

Changes sign, not magnitude of enthalpy change Demonstrates law of conservation of energy, true for all reversible reactions