topic 3 - revision

Question 1

chemical vs physical reaction

Answer 1

Chemical: rearranges the atoms into the new substances (still made up of the same elements that were present)
Physical: just a different state of the same substance

Question 2

how do you know if a reaction has occured

Answer 2

• a permanent colour change
• a gas is given off
• energy is either produced or absorbed (resulting in a temp change)
• a precipitate is formed
• one metal deposits on the surface of another

Question 3

how is a chemical equation formatted

Answer 3

reactants –> products

Question 4

what is a synthesis/combination reaction

Answer 4

where two or more reactants (A and B) combine to produce a single product (AB)

A + B –> AB
Zinc + Oxygen –> Zinc Oxide

Question 5

what is a decomposition reaction

Answer 5

where a compound is broken down into smaller compounds or separate elements (reverse of synthesis)

AB –> A + B
Iron Oxide –> Iron + Oxide

Question 6

what is a single replacement/displacement reaction

Answer 6

where a reactive element (a metal or a non-metal) and a compound react to produce another element and another compound. One of the elements in the compound is replaced by another element

A + BC –> B + AC (where A is metal)
(A is a metal and B is a metal cation and C is an anion)

Aluminium + lead (II) nitrate –> aluminium nitrate + lead

Question 7

what is a double displacement/precipitation reaction

Answer 7

where two ionic solutions react to produce two other ionic compounds. One of the compounds forms a precipitate, which is insoluble. The precipitate floats in the solution the settles and sinks to the bottom.

AB(aq) + CD(aq) –> AD(aq) + CB(s)
AgNO3(aq) + NaCl(aq) –> AgCl(s) + NaNO3(aq)

Question 8

what are spectator ions

Answer 8

the ions not involved in the formation of the precipitate

Question 9

what is a combustion reaction

Answer 9

the rapid reaction of a compound or element with oxygen to form an oxide and produce heat.

hydrocarbon + oxygen –> carbon dioxide + water

CH4 + O2 –> CO2 + H2O

Question 10

what is a neutralisation or acid rection

Answer 10

when an acid reacts with another substance and then they will neutralise each other

acid + bas –> salt + water

Question 11

what are the reactive metals

Answer 11

potassium
sodium
lithium
calcium

Question 12

what is the law of conservation of mass

Answer 12

the law of conservation of mass states that matter cannot be created or destroyed. This means that all atoms present as reactants and products must be in total remain constant

Question 13

balance Na + Cl2 –> NaCl

Answer 13

2Na + Cl2 –> 2NaCl

Question 14

how does the solid form in a precipitate reaction

Answer 14

when the two solutions are mixed, a pos ion and a neg ion combine to form an insoluble compound known as the precipitate.

Question 15

how do you predict the solid in a precipitate reaction

Answer 15

use the solubility table :)

Question 16

what is enthalpy (H)

Answer 16

enthalpy is the stored energy within the chemical bond.

Question 17

how do you find the change in enthalpy

Answer 17

(delta)H = H(products) - H(reactants)

Question 18

what happens during an exothermic reaction

Answer 18

• energy released
• during the chemical reaction, the bonds are broken and the atoms rearrange to form new chemical bonds
• temperature in created (delta T = pos)
• change in enthalpy = neg

Question 19

why is the change in enthalpy negative during an exothermic reaction

Answer 19

it is negative because there is less energy being stored and more energy being released into the surroundings

Question 20

what happens during an endothermic

Answer 20

• energy absorbed
• during the reaction, the reactant bonds are broken and the atoms rearrange to form new chemical bonds
• temperature decreases (delta T = neg)
• change in enthalpy = pos

Question 20

why is the change in enthalpy positive in endothermic reactions

Answer 20

it is positive because there is more energy being stored and absorbed hence making the change in enthalpy positive

Question 21

what is specific heat capacity

Answer 21

• the amount of heat required to raise the temperature of 1.00g of the substance by 1.00 degrees Celsius

Question 22

what is the formular for specific heat capacity

Answer 22

energy (j) = M x C x delta T

Question 23

what is metallic bonding

Answer 23

a metallic bond is the force of attraction between cations (metal and metal) and the delocalised electrons in the 3D lattice

Question 24

what is electronegativity

Answer 24

• the ability to hold onto electrons
• if metals have less than 4 electrons in outer shell it will prefer to lose electrons hence low electronegativity

Question 25

what are the properties of metals and the explanations of them

Answer 25

• malleable; bend into a shape - if a metal has an external force applied the cation and delocalised e’s can move into different shapes
• ductile; draw into a wire - same reason as malleable
• conductors of electricity and heat; free moving particles and heat transfers through 3D lattice - valance electrons are not firm within each atom and since the e’s are delocalised that are free to move and carry charge
• hard/strong/mpt and bpt; not easily broken - metallic bonds are strong
• lustrous; shiny
• sonorous; produce sound

Question 26

describe the reactivity of metals

Answer 26

• when a metal is placed into a solution with another metal compound, single displacement reactions may occur
• in these reactions the 2 metals compete to combine with the non-metal and the more reactive metal will win

Question 27

what is a redox reaction

Answer 27

• it involves the transfer of electrons from one species to the other
• it involves 2 half equations the reduction and oxidation equations

Question 28

which half equation is the loss of electrons and which is the gain of electrons

Answer 28

OIL - oxidation involves loss
oxidation - involves the loss of elections
electrons are on right side of equation

RIG - reduction involves gain
reduction - involves the gain of electrons
electrons are on left side of the equation

Question 29

what reaction is the oxidant in

Answer 29

the reduction half equation

Question 30

what reaction is the reductant in

Answer 30

the oxidation half equation

Question 31

what is the electrochemical series

Answer 31

• a table of relative oxidation and reduction strengths
• increase of reduction goes up the left side and increase in strength goes down the right side

Question 32

how do you know a chemical reaction has occurred according to the electrochemical series

Answer 32

the oxidant must be higher than the reductant or the line between them must be a negative gradient

Question 33

what are electrochemical cells

Answer 33

electrochemical cells are designed to make use of the displacement reactions by separating the two half reaction by making use of the electrical energy produced by the transfer of electrons

Question 34

what is the purpose of the salt bridge in the galvanic cells

Answer 34

required to balance the charge changes by providing more ions in each beaker and to complete the circuit

Question 35

what half equation will be the anode

Answer 35

oxidation

Question 36

what half equation be the cathode

Answer 36

reduction

Question 37

what is the oxidation number of an element in its natural form

Answer 37

zero

Question 38

what is the oxidation number of a changed particle

Answer 38

what ever the number of the charge is

Al+3 = 3
S-2 = -2

Question 39

oxidation number for hydrogen

Answer 39

in non-metal compounds = 1
in metal hydrides = -1

Question 40

oxidation numbers for oxygen

Answer 40

normal = -2
peroxide compounds = -1
bonded with fluorine = 2