chemistry

Question 1

Chemical reactions

Answer 1

bonds break and new ones are formed. Reactant particles rearrange to form product particles.

Question 2

Collision Theory

Answer 2

The first step in a chemical reaction is thought to involve a collision between the reactant particles. The collision theory states that for a collision between reactant particles to lead to a chemical reaction, the following conditions must be fulfilled:

1. The molecules must collide with sufficient energy to break the bonds of the reactant molecules. This is known as the activation energy.
2. The molecules must collide with an orientation that is suitable for the breaking of some bonds and the formation of others.

Question 3

Discuss different ways that reaction rates can be measured.

Answer 3

The rate of reaction can be observed by watching the disappearance of a reactant or the appearance of a product over time.

Question 4

Activation energy

Answer 4

Is the energy required to break existing bonds and form new bonds. If a collision occurs with more energy than the activation energy, the reaction will occur. The higher the activation energy, the more energy is required for a collision to be effective. The lower the activation energy, the less energy is required.

Question 5

Investigate factors that affect the rate of a chemical reaction

Answer 5

agitation, state of subdivision of reactants, temperature and concentration.

Question 6

Agitation

Answer 6

mixing or stirring can speed up the rate of reaction by exposing unreacted particles

• sometimes product particles build up on the reactants, like gas bubbles, and block the reactant particles from collision
• agitation can remove this build-up

Question 7

State of Subdivision (surface area)

Answer 7

• The smaller the particles in a reaction, the faster the reaction rate.
• Smaller particles means greater surface area exposed during reaction.
• If more reactant particles are exposed, there will be more particle collisions per
  second the same percentage of collisions are successful

Question 8

Temperature

Answer 8

An increase in temperature increases the average kinetic energy of the reactant molecules. There are two ways in which increasing the temperature leads to an increase in the reaction rate:

1. With more kinetic energy, the reactant particles move at greater speeds. As they are moving faster, they are more likely to collide. (more collisions will occur because the reactants are moving faster)
2. With more kinetic energy, a greater proportion of reactant particles have sufficient kinetic energy to supply the activation energy needed for the reaction. (more collisions will be effective because the reactants have higher energy)

Question 9

Catalysts

Answer 9

They can increase the rate of reaction in one of two ways-

1. By making it easier for collisions to occur
2. By decreasing the energy a collision needs to be effective

Question 10

Exothermic

Answer 10

When energy is released (light or heat)

Question 11

Endothermic

Answer 11

When energy is absorbed (melting)

Question 12

Atomic structure

Answer 12

• 1st shell- Holds 2 electrons
• 2nd shell- Holds 8 electrons
• 3rd shell- Holds 18 electrons
• A full outer electron shell = stable
• Atoms try to achieve a full outer shell by gaining or losing electrons to another atom. When losing electrons, the atom gains a positive charge. When gaining electrons, the atom gains a negative charge.

Question 13

Explain arrangement of elements in the periodic table into groups & periods.

Answer 13

• Atomic Number: number of protons (+) in the nucleus of an atom, electrons (-), neutrons are neutral.
• Rows are called periods- period number is equal to the number of electron shells - Columns are called groups-
  Group number: last digit reflects number of valence electron
  Valence electrons: electrons located in outermost electron shell

Question 14

g1 Alkali metals

Answer 14

• 1 valence electron
• loses 1 electron to become stable (full outer shell)
• forms ion with +1 charge
• soft metal, shiny when cut
• low melting point
• highly reactive
• react (violently) with water

Question 15

g2 Alkaline Earth Metals

Answer 15

• 2 valence electrons
• loses 2 electrons to become stable (full outer shell)
• forms ion with +2 charge
• relatively soft metal
• still have quite a low melting point
• very reactive
• react with water

Question 16

g17 Halogens

Answer 16

• 7 valence electrons
• gain 1 electron to become stable
• forms ion with -1 charge
• F and Cl are gases
• Br is a liquid
• I and At are solids
• moving down the group, elements become less reactive

Question 17

g18 Noble Gases

Answer 17

• full outer shell (stable arrangement)
• no charge
• very unreactive
• gas at room temperature

Question 18

• Explain the formation of ions and write simple ionic formulas

Answer 18

Metal Atoms: have 1,2 or 3 electrons in their outer shell, lose 1,2 or 3 electrons to achieve a full outer shell, in doing so gain a positive charge

Non-Metal Atoms (Group 15,16,17): have 5,6 or 7 electrons in their outer shell, gain 1,2 or 3 electrons to achieve a full outer shell, in doing so, gain a negative charge

Question 19

Monatomic Ion

Answer 19

Forms when a single atom gains or loses electrons in order to be stable

Question 20

Ionic Bonding

Answer 20

metal atoms lose electrons and form cations (+ve), non-metal atoms gain electrons and form anions (-ve), electrons are transferred from metal atoms to non-metal atoms and an ionic bond is formed.

Question 21

Ionic Formula:

Answer 21

shows the ratio of cations to anions, must be neutral – charges must balance.