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Chemical Change - Reactions. Objectives: At the end of this section you should be able to:- Explain the difference between chemical and physical change. Use the periodic table to determine valency. - PowerPoint PPT Presentation
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Chemical Change - ReactionsObjectives: At the end of this section
you should be able to:-• Explain the difference between chemical and physical
change.• Use the periodic table to determine valency.• Explain the significance of the law of constant
composition for writing chemical reactions.*** (comeback to)
• Write and balance chemical formulae.• Calculate reacting masses for given reactions.• Explain energy changes in reactions.• Explain Avogadro’s law.• Work out reacting volumes of gases.
Chemical Change - ReactionsObjectives: At the end of this section
you should be able to:-• Distinguish between synthesis and decomposition
reactions• Discuss how energy released by chemical reactions is
essential for life• Describe how metals react with oxygen• Explain the reverse process in which metals are
separated from their oxides• Describe the reactions of non-metals with oxygen• Write balanced equations for reactions involving non-
metals.
Physical and chemical change
Nitrogen separated from air by fractional distillation
Lightning causes nitrogen to react with air to form nitrogen
Physical and chemical change
Nitrogen separated from air by fractional distillation
Lightning causes nitrogen to react with air to form nitrogen
N2 (g) N2 (l)
Gas liquid
FormulaeCH4
CO2
Elements on the LEFT of the periodic table are written FIRST. If elements are above/below each other then the LOWER one is written FIRST.
H
SO
H2SS SO2S
SC
Consider the following analysis of different samples of table salt, what do you notice?
Hint??
Sample no.
Sample mass
Mass of Na
Mass of Cl
1 117g 46g 71g
2 468g 184g 284g
3 59g 23g 36g
Consider the following analysis of different samples of table salt, what do you notice?
Sample no.
Sample mass
Mass of Na
Mass of Cl
1 117g 46g 71g
2 468g 184g 284g
3 59g 23g 36g
Hint?? Ratios??
When elements combine with each other to form compounds, they always combine in an exact ratio and mass with one another.
Consider the following analysis of different samples of table salt:
Sample no.
Sample mass
Mass of Na
Mass of Cl
1 117g 46g 71g
2 468g 184g 284g
3 59g 23g 36g
The Law states:
A certain chemical compound always contains the ……………………. chemically combined in the ………… …………………….. by ……………………..
NaCl CaCl2 KMnO4 K2Cr2O7
Ratios: …….……….. ………. …………….
These ratios ………………. change.
NaCl is always 1:1 and 23g:35,5g – irrespective of whether the NaCl comes from the UK, USA or SA.
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.
Molecules
O2
a3CH4
b CO2
c
H2S
CH4 + 2O2 ---> CO2 + 2H2O
Methane + oxygen --> water + carbon dioxide
Conservation of Mass, Atoms & Molecules• Show that mass, atoms are conserved but molecules are not
H2 + O2 H2O
REACTIONSHydrogen and oxygen react to produce water.
H2 + O2 H2O
Ar:
Mr:
Balanced Eqn:
H2 + O2 H2O
LHS:
RHS:
LHS = RHS
MASS is CONSERVED!!
This is true for ALL REACTIONS.
This is the reaction used to power the space shuttle.
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.
REACTIONS
1. Butane reacts with oxygen 2. Carbon dioxide and water are formed
Butane + Oxygen ---> Carbon dioxide + water
C4H10 + O2 ---> CO2 + H2OWhat mass of carbon dioxide is produced from each
butane molecule?
1 2
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!
Reacting Masses
1. Na + Cl2 --> NaCl
2. C + Cl2 --> CCl4
3. ZnS + O2 --> ZnO + SO2
4. FeS + HCl --> H2S + FeCl2
5. SO2 + H2S --> S + H2O
Calculate the mass of each underlined compound either produced or required. (Balance the reactions first)
Volume - Volume Calculations
H2 + N2 --> NH3
If 3.00 dm3 of nitrogen are reacted to produce ammonia, what volume of hydrogen will be required? (At STP)
Volume - Volume CalculationsH2 + N2 --> NH3
If 3.00 dm3 of nitrogen are reacted to produce ammonia, what volume of hydrogen will be required? (At STP)
1. 3H2 + N2 --> 2NH3
2. n(N2) = v/Mv = 3/22.4 = 0.134mol
3. N2 : H2 1:3 n(H2) = 3(N2)
4. n(H2) = 3(0.13) = 0.401mol
5. v(H2) = n(H2)Mv = 0.401(22.4) = 8.98dm3
Balancing Reactions1. 2Na + Cl2 --> 2NaCl
2NaCl: 2(23+35.5) = 2(58.5)=117g
1. C + 2Cl2 --> CCl4
CCl4: 12 + 4(35.5) = 154g
1. 2ZnS + 3O2 --> 2ZnO + 2SO2
SO2: 2(32 + 2(16)) = 128g
1. FeS + 2HCl --> H2S + FeCl2
FeS: 56 + 32 = 88g
1. SO2 + 2H2S --> 3S + 2H2O
H2S: 2(2 + 32) = 68g
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
Balancing More Reactions
1. 2Na + 2H2O --> 2NaOH + H2
2. 2H2 + O2 --> 2H2O
3. CaCO3 --> CaO + CO2
4. CaCl2 + Na2SO4 --> CaSO4 + 2NaCl
5. 2Al(NO3)3 + 3K2CO3 --> Al2(CO3)3 + 6KNO3
6. 2Na3PO4 + 3MgI2 --> Mg3(PO4)2 + 6NaI
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 16 8 0 8
Water 10 0 20 10
TOTAL 26 8 20
butane