Module 3 - Reactive Chemistry

Question 1

Synthesis Reaction

Answer 1

A compound is formed from its constituent elements
e.g. S(g) + O2 (g) -> SO2 (g)

Question 2

Decomposition Reaction

Answer 2

One single compound breaks down into two or more simpler chemicals.
Decomposition of Zinc carbonate: ZnCO3(s) -> ZnO(s) CO2(g)

Question 3

Combustion Reaction

Answer 3

A substance reacts with oxygen and heat is released.
CH4(g) + 2O2(g) -> CO2(g) + 2H2O(g)

Question 4

Precipitation Reaction

Answer 4

A reaction between ions in a solution forming an insoluble compound (a precipitate)

Question 5

Acid/Base reaction

Answer 5

A neutralisation reaction
Metal hydroxide + acid -> water +salt
e.g. Ca(OH)2(aq) + H2SO4(aq) -> 2H2O(l) + CaSO4(aq)

Question 6

Acis/Carbonate reactions

Answer 6

Metal carbonate + acid -> water + carbon dioxide + salt
CuCO3(s) + 2HNO3(aq) ->H20(l)+ CO2(g)+Cu(NO3)2(aq)

Question 7

Electronegativity

Answer 7

This is a property that demonstrates a general trend across periods down groups of the periodic table.
Trend down - Electronegativity decreases
Trend across - electro negativity increases

Question 8

Atomic radius

Answer 8

Atomic radii tend to decrease moving from left to right across a period and increases going down the groups

Question 9

Ionisation Energy

Answer 9

Ionisation energy is a measure of the energy needed for an atom of an element to lose an electron.
The easier it is to remove an electron from an atom, the more reactive is the metal. Thus, the relative reactivity of metals is related to their ionisation energy.
GENERALLY: The activity of the metals increase as their ionisation energy decreases.

Question 10

Reactivity

Answer 10

The ease with which an element chemically reacts with different substances is called its reactivity.
Two groups of very active elements occur on either side of the most unreactive elements, noble gases.

Question 11

Metal reactivity

Answer 11

Generally metal that react vigorously with diluted acids also react vigorously with water and oxygen, often called ‘very active metals’, and less reactive metals are the ‘active metals’.
The metals that don’t react at all with dilute acids also don’t react with water or oxygen and are the ‘less active metals’

Question 12

Oxidation and Reduction

Answer 12

(Electron transfer reactions)
Oxidation and reduction reactions are simply chemical processes that involve the loss and gain of electrons.

A reaction that involves electron transfer is called a REDOX reaction.
Oxidation and reduction are complementary processes, they must occure together.
Many reaction involving metals are redox reactions

Question 13

Oxidation

Answer 13

OXIDATION = LOSS OF ELECTRONS (OIL)
In this particular type of reaction, the chemical species that LOSES the electrons is OXIDISED.

The chemical species that oxidation of another is called the oxidising agent (oxidant) and itself is reduced.

Question 14

Reduction

Answer 14

REDUCTION = GAIN OF ELECTRONS (RIG)
The chemical species that gains the electrons is said to have been reduced.

The chemical species that causes reduction of another is called the reductant and it is oxidised

Question 15

Oxidation number

Answer 15

1. The oxidation state of an element is an indication of the degree of oxidation than an atom has undergone. Each oxidation state has an oxidation number.
2. Oxidation number is used to indicate the positive or negative character of an atom when it is present.
   e.g Cl2 has a oxidation number of 0, but the ion Cl^- has a oxidation number of -1.
3. Oxidation numbers are allocated to the atoms in an element, ion or molecule according to the rules:
   -Uncombined elements have an oxidation number of 0. (Na, Cl4)
   -Oxygen has an oxidation number of -2 in compounds (except in peroxides and F2O)
   -Hydrogen has an oxidation number of +1 in compounds (except ionic hydrides).
   -In a species the sum of the oxidation numbers is equal to the charge of the species.
   -During redox reactions, one atom increases its oxidation number whilst another atom decreases.

Question 16

Galvanic Cells

Answer 16

A galvanic cell is a device constructed so oxidation and reduction reactions are physically separated but are connected by an external circuit (conductor) which carries electrons and a salt bridge which carries charged ions in solution (completing the circuit).

the energy of the moving electrons is electrical energy that can be used to turn an electric motor, produce heat and/or light energy.

Galvanic cells allow a redox reaction to take place in such a way that electricity is produced in an external circuit.
ANODE - the electrode at which oxidation occurs
CATHODE - the electrode at which reduction occurs

Question 17

Electricity from Spontaneous Redox

Answer 17

Spontaneous redox reactions involve a transfer of electrons from one reactant to another, there is electron flow between species but no electricity produces.

Question 18

Standard Reduction Potential

Answer 18

A numerical measure (volts) of the relative tendency of an electrode (half cell) to be reduced compared with the standard hydrogen (electrode) half cell.
*Standard reduction potentials are tabulated on the HSC datasheet

Question 19

Calculating Standard Reduction Potentials

Answer 19

The hydrogen electrode is a reference electrode.
Every other half cell voltage has been measured compared to this reference electrode, thus we can calculate the voltage (SRP) between any two electrodes without actually measuring the voltage.

Steps in calculating SRP
1. Determine the oxidation and reduction half reaction. The electrode half equation with a higher potential will occur as written (it will occur at the cathode).
2. Reversing the reduction half equation with the lower reduction potential changes the E° sign, this is the oxidation half equation.
3. Balance the half reactions and add them to get overall redox reaction. Changing coefficients in order to balance the equations has no effect on E° value.
4. Add E° to obtain overall theoretical galvanic cell voltage.

In other words :E°(total) = E°(cathode) + E° (anode)

Question 20

What effects rates of Reaction

Answer 20

Chemical reactions will occur at a fast rate with a higher temperature concentration of reactant, surface area of the reactant and the catalysts used.

Question 21

Activation energy