C3

Define Endothermic and Exothermic reactions

Endothermic- energy taken in to break the bonds in the reactants is more than the energy given out when new bonds are made in products
Exothermic- energy taken in to break the bonds in the reactants is less than the energy given out when new bonds are made in products

Define Activation energy

Activation energy- the minimum energy needed to start a reaction

Difference in temperature of surroundings between an Endothermic and exothermic reaction

Endothermic- the temperature of the surroundings decrease
Exothermic- the temperature of the surroundings increase

How do you calculate bond energy?

1. Find the total energy of the bonds broken in reactants (include number at front)
2. Find the total energy of bonds formed in products
Energy change = energy in reactants - energy in products
If it is negative then it is exothermic

Know these polyatomic ions

Carbonate- CO3 (charge 2-)
Nitrate- NO3 (charge 1-)
Hydroxide- OH (charge 1-)
Sulfate- SO4 (charge 2-)

What is the value of avogodra’s constant?

6.02×10²³

How do you calculate the moles of a substance?

Moles= number of particles/avogodra’s constant
Moles = mass/Mr

How to calculate reacting masses?

1. Find out moles of substance mentioned using mass/Mr
2. Find out amount of moles of the other substance (doesn’t state its mass) using Molar ratio (eg. 2:1)
3. Find the mass using mass= moles x Mr

How to find the limiting reactant?

1. Find out moles of both substances using moles = mass/mr
2. Find out theoretical moles of one of the substances using the molar ratio
3. If theoretical moles > actual moles then that substance is the limiting reactant. If actual > theoretical then other substance is limiting reactant
4. Use mass = moles x Mr to find out mass of product formed (use the limiting reactant as your no. of moles)

Difference between covalent bonding and ionic bonding?

Covalent- if a compound is made from 2 non-metals
Ionic- if a compound is made from a metal and non-metal

Define oxidation and reduction

Oxidation- When an element loses electrons to form a positive ion
Reduction- when an element gains electrons to form a negative ion

In an ionic equation what state are the products and reactants in?

Reactants- Aqueous (aq)
Products- precipitate so solid (s)

Which acids form which salts (acids react to form a salt)

Hydrochloric acid- Metal chloride
Nitric acid- metal nitrate
Sulfuric acid- metal sulfate

Acid + metal = ?

Acid + metal = salt + hydrogen
Sodium + Hydrochloric acid = sodium chloride + hydrogen

Acid + base = ?

Acid + base = salt + water (+ carbon dioxide if base is carbonate)
Sodium oxide + Nitric acid = Sodium Nitrate + water
Sodium Carbonate + Nitric acid = Sodium Nitrate + water + carbon dioxide

What are bases?

Bases are solids that are metal oxides or metal carbonates. They neutralise acids

What are alkalis?

Alkalis are aqueous solutions that are group 1 metal hydroxides and they neutralise acids

Acid + Alkali = ?

Acid + Alkali = salt + water
Sodium hydroxide + hydrochloric acid = sodium chloride + water

Difference between a strong and weak acid?

A strong acid FULLY ionises in water whilst a weak acid only partially ionises in water. A strong acid releases a high concentration of H+ ions whilst a weak acid releases a low concentration

Difference between a concentrated and dilute acid

A concentrated acid has more moles of acid molecule in 1dm³ of water (more acid less water.) Dilute acid the opposite

How does the pH of an acid change

If the concentration of a strong acid increases by a factor of 10, the pH decreases by 1

Difference between a cation and anion

Cation- a Positive ion
Anion- a negative ion

What does a negative electrode and positive electrode attract

Negative electrode (Cathode) attracts positive ion (cation)
or H+
Positive electrode (Anode) attracts negative ions (anions) or OH-

When does OH- get attracted to anode and H+ to cathode

OH- gets attracted if the negative ion in the electrolyte is not in group 7
H+ - gets attracted if it less reactive than the positive ion in the electrolyte

How do you make a soluble salt (6 marks)?

1. React your acid with excess metal carbonate or metal oxide to ensure all acid fully neutralises
2. Filter off the excess base
3. Place salt solution in evaporating dish
4. Place dish in water bath to crystalise it
5. Heat until it reaches crystallisation point and cool crystals
6. Filter the crystals, wash them and dry them (on windowsill for example)

Difference between the reducing agent and oxidising agent

Reducing agent- the one that loses an electron (oxidises)
Oxidising agent- the one that gains an electron (reduces)