Chemistry Module 3

what are the signs of a chemical reaction?

• colour change

• production of a gas

• formation of a precipitate

• heat gain/loss

what do synthesis reactions involve?

involve (smaller) elements or compounds combining to form larger compound

iron + sulfur → ?

iron sulfide

define oxidisation

reacting with oxygen

magnesium + oxygen → ?

magnesium oxide

what are synthesis reactions used to produce?

neoprene (plastic used in gloves) & kevlar (polymer used to make bullet-proof jackets)

what is the synthesis reaction for ammonia?

N_2(g) + H_2(g) → NH_3(g)

what is the synthesis reaction for ammonium sulphate?

[synthesis reaction for ammonia] + [S_(l) → SO_2(g) → SO_3(g) → H₂SO_4(l) = (NH₄)₂SO_4(s)

what are the roles of ammonia?

• fertilisers

  • combined with sulfuric acid produces the fertiliser ammonium sulphate

  • fertiliser ensures better crop yields, allowing more people to be fed & reducing starvation

• explosives

  • used as the starting material to make explosive nitrate

  • production of TNT & dynamite allowed for countries to wage wars

what does decomposition involve?

involve large compound decomposing into smaller elements/compounds

water → ?

hydrogen + oxygen

define electrolyiss & what it is used for + relevant equation

• decomposition using electrical energy

• used to decompose water to oxygen & hydrogen

  • equation: 2H₂O_(l) → 2H_2(g) + O_2(g)

• also used to produce commercial supplies of reactive metals

  • in Australia, aluminium smelters electrolyse bauxite (Al₂O₂) to produce aluminium metal in large quantities

define photolysis & give examples of products that reduce photolysis

• decomposition using light energy

• hydrogen peroxide is sold in an opaque container to improve shelf life

• cooking oils & other food items are sold in dark glass containers to limit decomposition caused by light passing through liquid

how do photographers produce permanent images? give a relevant equation

• photographers harnessed the decomposition of silver compounds to produce permanent images

  • silver bromide on photographic films decomposes to silver when light enters the camera

  • equation: 2AgBr_(s) → 2Ag_(s) + Br_2(g)

  • silver atoms form an image that is enhanced when the film is developed

define thermal decomposition

process by which heat breaks down compounds into simpler substances

what does decomposition require?

energy; heating is an obvious way to supply energy

what happens to most carbonate compounds when heated

most carbonate compounds will decompose when heated, releasing CO₂ gas

give the equation & what happens when calcium carbonate is heated

• CaCO_3(s) → CaO_(s) + CO_2(g)

• Calcium oxide formed (aka lime) is used to mark football pitch lines to & reduce acidity of soil

give the equation & what happens when sodium azide is heated + its purpose/use

• 2NaN_3(s) → 2Na_(s) + 3N_2(g)

• Used to save lives by inflating vehicle airbags

• Collision in modern vehicle triggers rapid heating of sodium azide → decomposition produces large volumes of nitrogen gas → airbag inflates to protect vehicle occupants

what does combustion require?

• fuel to burn

• oxygen for fuel to burn in

• energy to get process started

what do reactants combine with & what is released during combustion

• reactant combines with oxygen (oxidisation)

• thermal energy is release during combustion

define hydrocarbon + what does combustion of a hydrocarbon produce?

combustion of a hydrocarbon (compound containing only carbon & hydrogen) produces carbon dioxide & water, provided there is enough oxygen present

write & balance the equation of propane C₃H₈ + what it is a major component of

• major component of LPG, BBQ bottled gas

• C₃H_8(g) + 5O_2(g) → 3CO_2(g) + 4H₂O_(l) + heat

• balancing order:

1. carbon

hydrogen

oxygen

what happens in combustion when sufficient oxygen is available?

complete combustion occurs & carbon dioxide is produced

• blue flame on bunsen burner

what happens when there is less oxygen available in combustion?

products of incomplete combustion are produced (carbon monoxide & carbon as soot)

• yellow flame on bunsen burner

define precipitate

insoluble compound formed when two clear solutions mix together to form a solid

what do precipitation reactions involve?

pairs of solutions reacting to produce a solid

sodium chlorise + silver nitrate → ? (give chemical equation as well)

• sodium nitrate + silver chloride (s)

• NaCl_(aq)      +   AgNO_3(aq)   →    NaNO_3(Aq)      +       AgCl_(s)

what does each ionic solution contain?

pair of ions:

• cation

• anion

are all ionic compounds equally soluble?

no

what does the solubility of a precipitate formed depend on?

solubility rules

what happens when sodium chloride solution reacts with silver nitrate?

positive silver & negative nitrate ions ‘meet’ positive sodium & negative chloride ions → positive silver & negative chloride ions form insoluble precipitate