chemical reactions
DESCRIPTION
A set of slides created to teach Chemical Reactions to learners at Bishops Diocesan College in Cape Town.TRANSCRIPT
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Physical & Chemical Change
K Warne
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Phases of MatterPhases of Matter
PLASMAPLASMA+
++ + +
+
The FOUR states of matter are determined by the amount of ………………….…………………. available.
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Melting (Fusion)When a solid melts the particles
need to undergo a number of changes:
Solid --> Liquid:– the spaces between the particles
increase– The energy of the particles
increases– The forces between the particles are
weakened
Each of these changes requires energy to be put in.
The temperature stays constant because the extra energy is being used to weaken the forces.
Melting
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Boiling vs Evaporation
Wind
Water molecules (high energy) escape from the surface of the liquid.
The remaining particles have less energy - lower temperature
ENERGY IS REMOVED FROM THE WATER (Cooling Effect).
All liquids have their own vapour (gas).
This vapour has a pressure which increases with temperature.
When the vapour pressure equals the pressure outside the liquid the liquid boils.
GAS
LIQUID
IN BOILING ENERGY MUST
BE PUT IN.The temperature of the water does not change as the energy is used to change the phase.
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Intermolecular Forces broken!
Phase Changes
Wind
Forces between particles (intermolecular) breaking.
GAS
OH
H
OH
H
OH
H
O H
H
OH
H
Bonds inside particles (intramolecular) do NOT break!
Boiling & evaporation are both phase changes – intermolecular bonding is involved (broken or formed) in phase changes
– intramolecular bonding is not affected!
Molecule escapes!
High energy molecules escape!
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Boiling vs Evaporation
Boiling Evaporation
Similarities • Change water to water vapour• Particles undergo same changes (increase spaces, energy, weaker forces)
Differences • High Temp• Energy put in• Affected by atmospheric pressure
• Low Temp• Energy taken
out.• Not affected by
pressure.
Consider the following analysis of different samples of table salt (NaCl) , what do you notice?
Sample no.
Sample mass
Mass of Na
Mass of Cl % Na %Cl
1 117g 46g 71g 46*100
117
=39.3%
2 468g 184g 284g 184*100
284
3 59g 23g 36g
1. 117g (46g Na & 71g Cl)
The Law states:
A certain chemical compound always contains the same elements chemically combined in the same proportions by mass.
NaCl CaCl2 KMnO4 K2Cr2O7
Ratios: 1:1 1:2 1:1:4 2:2:7
These ratios never change.
NaCl is always 1:1 and 23g:35,5g – irrespective of whether the NaCl comes from the UK, USA or SA.
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Conservation of Mass, Atoms & Molecules• Show that mass, atoms are conserved but molecules are not
2H2 + O2 2H2O
2H2 O2 2H2O
Atoms 4 2 = 6 6=6 Conserved
Mass 4 32 = 2x18 36=36 Conserved
molecules 2 1 = 2 3≠2 Not conserved!
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REACTIONSHydrogen and oxygen react to produce water. (Synthesis reaction)
H2 + O2 H2O
Ar: H = 1, O = 16
Mr: H2 =2, O2 = 32
H2O = 16+2=18
Balanced Eqn:
2H2 + O2 2H2O
LHS: RHS:
2(2) + 32 = 36 2(2+16) = 36
LHS = RHS
MASS is CONSERVED!!
This is true for ALL REACTIONS.
This is the reaction used to power the space shuttle.
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REACTIONS
1. Butane reacts with oxygen 2. Carbon dioxide and water are formed
Butane + Oxygen ---> Carbon dioxide + water
2C4H10 + 13O2 ---> 8CO2 + 10H2O
1 2
Reaction equation BALANCED!
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Balancing Reactions1. 2Na + Cl2 --> 2NaCl
2NaCl: 2(23+35.5) = 2(58.5)=117g 1.2x10-6
1. C + 2Cl2 --> CCl4
............................................................................
1. 2ZnS + ...O2 --> ...ZnO + ...SO2
............................................................................
1. FeS + ...HCl --> H2S + FeCl2
............................................................................
1. SO2 + ...H2S --> ...S + ...H2O
............................................................................
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Balancing More Reactions
1. Na + H2O --> NaOH + H2
2. H2 + O2 --> H2O
3. CaCO3 --> CaO + CO2
4. CaCl2 + Na2SO4 --> CaSO4 + NaCl
5. Al(NO3)3 + K2CO3 --> Al2(CO3)3 + KNO3
6. Na3PO4 + MgI2 --> Mg3(PO4)2 + NaI
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BALANCING REACTIONS
1. Butane reacts with oxygen
1 2
Reactants
Substance O C H No.
oxygen 26 13
butane 0 8 20 2
TOTAL 26 8 20
2. Carbon dioxide and water are formed
Products
Substance O C H No.
Carbon dioxide
Water
TOTAL
butane
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Hi -
This is a SAMPLE presentation only.
My FULL presentations, which contain loads more slides and other resources, are freely available on my resource sharing website:
www.sciencecafe.org.za
(paste into your browser if link above does not work)Have a look and enjoy!
Keith Warne