y8 chemical reactionsss

Question 1

key signs of a chemical reaction

Answer 1

-colour change
-changes temp by itself
-flame/explosion
-solid produced without cooling
-gas produced without heating

Question 2

difference between physical and chemical reaction

Answer 2

physical-no bonds broken/formed
chemical-bonds break/form to create new chemicals

Question 3

when balancing chemical reactions, what cannot be changed

Answer 3

numbers after a chemical eg. O2

Question 4

what is a balanced chemical reaction

Answer 4

same number of atoms of an element in reactants and products

Question 5

what is wrong with the equation:
2Ca + O2 = 2CaO

Answer 5

there should be a –> instead of an =
the 2 after O should be small (in subscript)

Question 6

what is an exothermic reaction

Answer 6

temp of surroundings increases (reaction is releasing heat into surroundings, transferring energy from chemical store to thermal)

Question 7

what is an endothermic reaction

Answer 7

temp of surroundings decreases (reaction is absorbing heat from surroundings, transferring energy from thermal store to chemical)

Question 8

oxidation

Answer 8

when an element combines with oxygen to form a compound

Question 9

combustion

Answer 9

when a fuel rapidly reacts with oxygen, transferring energy to the thermal store of the surroundings (high temperature)

Question 10

acid

Answer 10

H+ ions

Question 11

alkaline

Answer 11

OH- ions

Question 12

what do all alkali metals have in common

Answer 12

one electron in outer shell

Question 13

what do all halogens have in common

Answer 13

one gap in outer shell (seven electrons)

Question 14

what do all noble gases have in common

Answer 14

full outer shell

Question 15

why are certain metals used for jewellery

Answer 15

very unreactive-don’t tarnish

Question 16

reactivity series

Answer 16

potassium
sodium
calcium
magnesium
aluminium
(carbon)
zinc
iron
tin
lead
(hydrogen)
copper
gold
silver
platinum

Question 17

what is the other name for hydrogen ______ eg. hydrogen sulfate

Answer 17

______ acid eg. sulfuric acid

Question 18

metal + acid

Answer 18

salt + hydrogen

Question 18

catalyst

Answer 18

chemical that speeds up a reaction without being part of reaction (doesn’t change throughout)

Question 19

metal carbonate + acid

Answer 19

salt + water + carbon dioxide

Question 19

acid + alkali

Answer 19

salt + water

Question 20

biological catalyst example

Answer 20

enzyme eg. amylase, protease etc.

Question 21

catalysts are very…

Answer 21

specific to a particular reaction

Question 22

the most common catalyst works by…

Answer 22

binding both reactants and holding them together in the correct orientation to react

Question 23

why is the inside of a catalytic converter a honeycomb structure

Answer 23

metal is expensive, need as large a surface area as possible (to bind reactants), but a minimal amount of metal, so you coat a thin layer of metal onto the honeycomb

Question 24

what happens in a physical change

Answer 24

the state changes eg. solid to liquid, but this is done with heating/cooling, not by itself

Question 25

rusting is an example of what type of chemical reaction

Answer 25

oxidation

Question 26

are metal oxides acidic or alkaline

Answer 26

alkaline

Question 27

what happens when a compound combusts

Answer 27

each element in the compound forms an oxide (oxygen is added to every element)

Question 28

thermal decomposition is when

Answer 28

a compound is broken down by heat

Question 29

neutralisation

Answer 29

when an acid's H+ ions react with an alkali's OH- ions to form water (H2O, two hydrogens one oxygen)

Question 30

displacement

Answer 30

a more reactive metal takes the place of a less reactive metal in a compund

Question 31

what is a salt

Answer 31

hydrogen ions in an acid have been replaced by a metal

Question 32

catalysts ___________ the _________ barrier which ___________

Answer 32

decrease energy increases the rate of reaction

Question 33

diatomic elements

Answer 33

are in pairs eg. oxygen, nitrogen, hydrogen - any group seven element (halogen)

Question 34

are all combustion reactions oxidation reactions

Answer 34

yes

Question 35

where are many catalysts found on the periodic table

Answer 35

transition metals (middle)

Question 36

if a less reactive metal is added to a salt solution containing a more reactive metal, what will happen

Answer 36

nothing (no reaction)

Question 37

pH 0 is a strong..

Answer 37

acid

Question 38

pH 14 is a strong..

Answer 38

alkali

Question 39

what are positive ions

Answer 39

positive ions (cations) are usually created when an atom or molecule loses electrons. The metals in Group 1 and 2 can easily lose electrons to become positively charged ions

Question 40

what are negative ions

Answer 40

Negative ions (anions) are usually created when an atom or molecule gains electrons. The non-metals in Group 7 are most likely to gain electrons to fill up their electron shell and become negatively charged.

Question 41

if an atom gains electrons, what charge does the resulting ion have (it works vice versa)

Answer 41

negative

Question 42

non-metal atoms always gain electrons to form negative ions. E.g. F atom (2,7) → F- ion (2,8) group 1 metals always lose 1 electron to form single positive ions. E.g. Na atom (2,8,1) → Na+ ion (2,8)

Answer 42

so the top right small numbers are about how many electrons the atom actually had before it gained a full outer shell

Question 43

materials with ionic bonds usually

Answer 43

have high melting points only conduct electricity when molten/dissolved

Question 44

the relative formula mass is equal to...

Answer 44

the sum of the relative atomic masses of every atom in a formula

Question 45

how to find the relative formula mass

Answer 45

1.) identify the relative atomic masses of each element in a compound 2.) multiply the relative atomic mass by the number of atoms of that element 3.) add up the results of each element

Question 46

reduction and oxidation

Answer 46

if a substance loses oxygen, it has been reduced, and the opposite if it has been oxidised

Question 47

a more reactive metal is one that..

Answer 47

forms positive ions more easily

Question 48

what is an alloy

Answer 48

an alloy is a combination of 2+ elements, where at least 1 is a metal. The ions of the different elements are different sizes. This makes it harder for the layers to slide across each other when a force is applied to the alloy. This makes alloys stronger than pure metals, and so they are often used in construction.

Question 49

common alloys

Answer 49

brass, aluminium, bronze, gold, steel