Chemistry

Question 1

Define a combustion reaction.

Answer 1

The reaction of a substance (fuel) with air, generally at high temperatures.

Question 2

What is the word equation for combustion? Include an example.

Answer 2

Fuel + Oxygen (O2) –> Carbon dioxide (CO2) + water (H20)
E.g., Methane + Oxygen –> Carbon dioxide + Water

Question 3

What happens during a combustion reaction and what are generally biproducts of this reaction?

Answer 3

Occurrences - Atoms of the element rearrange to join with oxygen atoms. These are often called oxides.
Biproducts - Heat, light.

Question 4

What type of reaction is a combustion reaction?

Answer 4

Fast, exothermic chemical reaction - irreversible, double displacement.

Question 5

Define a corrosion reaction.

Answer 5

The reaction of a metal with oxygen to form a new substance (metal oxide).

Question 6

What is the word equation for corrosion? Include an example.

Answer 6

Metal + Oxygen (O2) –> Metal oxide
E.g., Iron + Oxygen –> Iron oxide

Question 7

What happens during a corrosion reaction and what can be a catalyst?

Answer 7

Occurrences - The metal is slowly broken down
Catalyst - Water and higher temperatures can act as a catalyst throughout this reaction.

Question 8

What type of reaction is a corrosion reaction?

Answer 8

Slow (depends on metal reactant), exothermic chemical reaction - irreversible, synthesis/composition.

Question 9

Define a precipitation reaction.

Answer 9

A reaction which only occurs in solution - it is the mixing of two aqueous solutions to form an insoluble solid (precipitate)

Question 10

What is the word equation for precipitation? Include an example.

Answer 10

Soluble salt (aq) + Soluble salt (aq) –> Insoluble salt (s) + Soluble salt (aq)
E.g., Silver nitrate (aq) + Potassium chloride (aq) –> Silver chloride (s) + Potassium nitrate (aq)

Question 11

What happens during a precipitation reaction and what are generally products of this reaction?

Answer 11

There is an exchange between ionic compounds to form a double displacement reaction - creating one (or more) solid/s and an aqueous solution.

Question 12

What type of reaction is a precipitation reaction?

Answer 12

Irreversible :/, chemical reaction, double displacement can be either endothermic or exothermic - generally exo.

Question 13

What is the general equation for a decomposition reaction?

Answer 13

AB –> A + B
E.g., Hydrogen peroxide:
2H2O2 (aq) –> O2 + 2H2O

Question 14

What is the general equation for a composition/synthesis reaction?

Answer 14

A + B –> AB

Question 15

What is the general equation for a single displacement reaction?

Answer 15

AB + C –> AC + B

Question 16

What is the general equation for a double displacement reaction?

Answer 16

AB + CD –> AC + BD

Question 17

What are the 3 main acid reactions?

Answer 17

Acid + Base –> Salt + Water
Acid + Metal –> Salt + Hydrogen gas
Acid + Carbonate –> Salt + Water + Carbon dioxide

Question 18

What is a neutralisation reaction and why does it happen?

Answer 18

An Acid + Base reaction. The hydrogen ions (H+) in acids are ‘cancelled out’ by the hydroxide ions (OH-) in bases (alkalis).

Question 19

What are the 4 states of matter?

Answer 19

Solid (s), Liquid (l), Gas (g), Aqueous (aq).

Question 20

How can hydrogen gas be tested for?

Answer 20

Using the ‘pop’ test - a match is held over the reaction (usually completed in a test tube) often with a cork. If the cork ‘pops’ off when match heats it up, hydrogen is present.

Question 21

What is an element, atom, molecule, compound and mixture?

Answer 21

Element - Contains only ONE type of atom.
Atom - A single particle of an element.
Molecule - Substances that contain chemical bonds.
Compound - Contains more than one type of atom (element) and are chemically bonded.
Mixture - A combination of elements or compounds together without being chemically bonded.

Question 22

What is an ion?

Answer 22

A charged atom - can be either positively (cation) or negatively (anion) charged.

Question 23

Describe the layout of an element on the periodic table.

Answer 23

Element (centre), Atomic mass - protons + neutrons (below element), Atomic number - protons/electrons (top left corner).

Question 24

Cations are…?
Anions are…?

Answer 24

Cations are metals and are positively charged atoms.
Anions are non-metals and are negatively charged atoms.

Question 25

What are ionic and covalent bonds?
EXT.

Answer 25

Ionic bonds are between a metal (cation) and a non-metal (anion).
Covalent bonds are between two non-metals.

Question 26

What is a signal for corrosion?

Answer 26

Colour change.

Question 27

What is an endothermic reaction and how does it occur? Give an example of an endothermic reaction.

Answer 27

An endothermic reaction is where: during a chemical reaction, the reactants do not have enough activation energy to complete, so they take it from the environment, making the environment colder.
E.g., photosynthesis.
(energy needed to break reactant bonds < energy needed to form product bonds)

Question 28

What is an exothermic reaction and how does it occur? Give an example of an exothermic reaction.

Answer 28

An exothermic reaction is where: during a chemical reaction, the reactants have more energy than is required for the reaction to complete, so they release it into the environment, making the environment warmer.
E.g., respiration.
(energy needed to break reactant bonds > energy needed to form product bonds)

Question 29

What is matter?

Answer 29

Anything that has mass and takes up space (has a volume).

Question 30

What is the law of conservation of mass?

Answer 30

• In a chemical reaction, matter is NOT created or destroyed.
• New substances are formed due to the rearrangement of atoms.
• The mass remains constant.

Question 31

What groups (columns) in the periodic table can be precipitates?

Answer 31

Group 1 - NOT precipitates.
Group 17 - CAN be precipitates.

Question 32

What is the chemical equation for a photosynthesis reaction?

Answer 32

Carbon dioxide + Water –> Glucose + Oxygen

Question 33

What is the chemical equation for a respiration reaction?

Answer 33

Glucose + Oxygen –> Carbon dioxide + Water

Question 34

How can carbon dioxide gas be tested for?

Answer 34

Bubble the gas (CO2) into limewater (e.g., aq calcium hydroxide solution) - if it turns cloudy/milky white the gas is present. In this example a precipitate is formed.

Question 35

What is the balanced equation for photosynthesis (reversed for respiration)

Answer 35

P - 6CO2 (g) + 6H2O (l) –> C6H12O6 (s/l) + 6O2 (g)
R - C6H12O6 (s/l) + 6O2 (g) –> 6CO2 (g) + 6H2O (l)

Question 36

What are the 5 factors affecting rate of reaction?

Answer 36

CATALYSTS - lower the required activation energy, increased catalyst % increases rate of reaction.
SURFACE AREA - decreased surface area –> particles are more spread out –> cover more area –> collisions occur more frequently.
CONCENTRATION - higher concentration of reactants –> higher opportunity for collisions –> higher rate of reaction. High concentration = Concentrated. Low concentration = Dilute.
TEMPERATURE - Higher temperatures increase kinetic energy –> reach activation energy faster –> faster rate of reaction.
VOLUME/PRESSURE - lower volume –> less space –> increased collisions –> higher rate of reaction

Question 37

What is concentration - ext?

Answer 37

The number of solute particles per unit of solvent e.g., ‘more particles in the same volume of solution’.

Question 38

What is the rate of reaction?

Answer 38

The rate of a reaction is how quickly reactants are converted into products.

Question 39

What is the particle model?

Answer 39

The particle model states that all matter is made up of particles.

Question 40

What is the law of conservation of matter?

Answer 40

That matter is NEVER created or destroyed. Atoms only rearrange to form new substances.