energetics
TRANSCRIPT
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PlanningEnergetics
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Standard enthalpy change of neutralisation0 Definition0 Dependent variable0 Independent variable0 Value of Hneut
o
0 Basicity of acids
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Typical Experimental Set-up
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For each set of data
Amt. of HCl
Amt. of NaOH
Initial temp. of HCl
Initial temp.of NaOH
Ave. initial temp.
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Typical Table of Data
Amt. HnX Amt. NaOH
Max. temp.
T = Tmax - Tinitial
50 1040 2030 3020 4010 50
For example, using 1 mol dm-3 acid and NaOH
HnX + nNaOH NanX + nH2O
Better than the word “Final”
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Typical Graph – type 1
Vol. of NaOH used / cm3
10 2030
40 50
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If Basicity of acid, n = 1
Amt. HnX Amt. NaOH
Max. temp.
T = Tmax - Tinitial
50 1040 2030 3020 4010 50
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Work out using HClAmt. HCl Amt.
NaOHHneut
o
50 10 - 60 x c x T1
0.0140 20 - 60 x c x T2
0.0230 30 - 60 x c x T3
0.0320 40 - 60 x c x T2
0.0210 50 - 60 x c x T1
0.01
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Typical Graph – type 2
Vol. of NaOH used / cm3
10 2030
40 50
Type 1
Type 2
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If Basicity of acid, n = 2
Amt. HnX Amt. NaOH
Max. temp.
T = Tmax - Tinitial
50 1040 2030 3020 4010 50
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Work out using H2SO4
Amt. H2SO4
Amt. NaOH
Hneuto
50 10 - 60 x c x T1
0.0140 20 - 60 x c x T2
0.0230 30 - 60 x c x T3
0.0320 40 - 60 x c x T4
0.0410 50 - 60 x c x T2
0.02
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Most informative region
Vol. of NaOH used / cm3
10 2030
40 50
Type 1
Type 2
Monobasic
Dibasic
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Considerations for accuracy and
reliability0 Insulation – styrofoam cup, lid0 Stability of set-up – beaker0 thermometer – precision0 Consistency of stirring
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Standard enthalpy change of combustion
0 Definition0 Dependent variable0 Independent variable
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Typical Experimental Set-up
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Typical Table of Data
For example,CnH2n+2O + O2 nCO2 + (n+1)H2O
Initial mass of spirit
lamp
Final mass of spirit
lamp
Initial temp
Max. temp.
Raw Data
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Work out using C2H5OH
Mass of C2H5OH
T Hcombustiomo
- mH2O x c x TnC2H5OH
Processed Data
Refer to HCI/2010 for consideration on heat absorbed by Cu can.
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Considerations for accuracy and
reliability0 Heat loss to surroundings –
insulation of Cu can0 Heat loss to Cu can – consider
heat capacity of Cu can0 Incomplete combustion of alcohol
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If diff alcohols are used
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Standard enthalpy change of reaction
0 Definition0 Dependent variable0 Independent variable
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Na2CO3(s) + 2HCl(aq) 2NaCl(aq) + H2O(l) + CO2(g)
Suitable quantities of reactants to use: 0.010 mol Na2CO3 (1.06 g Na2CO3)
0.020 mol HCl ( 20 cm3 1 mol dm-3 HCl)
Mass of empty weighing bottle =
Mass of weighing bottle and Na2CO3=
Mass of emptied weighing bottle and residue
=
Volume of HCl used =
Initial temp of HCl =
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Typical Experimental Set-up
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Table of dataTime / min Temperature /
oC012
3.54567
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Typical graph
Temp / oC
Time / min1 23.5
4 5 6 7
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23.5
Temp / oC
Time / min
T
At 3 min, time of addition of Na2CO3
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Calculate Hreactiono
Hreactiono = - MHCl x c x T
nNa2CO3
Assume density of HCl = 1 g cm-3
Na2CO3(s) + 2HCl(aq) 2NaCl(aq) + H2O(l) + CO2(g)
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NaHCO3(s) + HCl(aq) NaCl(aq) + CO2(g) + H2O(l)
T
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Calculate Hreactiono
Hreactiono = + MHCl x c x T
nNaHCO3
Assume density of HCl = 1 g cm-3
NaHCO3(s) + HCl(aq) NaCl(aq) + H2O(l) + CO2(g)
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Think about…
0 The standard enthalpy change of:
Na2CO3(s) + HCl(aq) NaHCO3(aq) + NaCl(aq)