The petrol, can be represented by the formula of the octane rating, has earth specifies 704 g/L. Estimate the enthalpy variation when burning 28.5 liters of petrol, assuming energies of connection
0 = 0 (117 kcal)
C = 0 (173 kcal)
0–H (111 kcal)
C–C (83 kcal)
C–H (99 kcal).
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To estimate the enthalpy variation when burning 28.5 liters of petrol, we need to calculate the total energy released during the combustion process.
First, we need to determine the chemical composition of petrol. By the given information, we can assume petrol is composed of hydrocarbons with an average octane rating. Taking the average octane rating to be C8H18, we can calculate the molecular weight of petrol as follows:
Molecular weight of octane (C8H18) = (12 * 8) + (1 * 18) = 114 g/mol
Next, we can calculate the molar concentration of petrol using its density:
Density of petrol = 704 g/L
Molar concentration = Density / Molecular weight
= 704 g/L / 114 g/mol
= 6.18 mol/L
Now, we can calculate the number of moles of petrol in 28.5 liters:
Number of moles of petrol = Molar concentration * Volume
= 6.18 mol/L * 28.5 L
= 176.13 mol
To determine the enthalpy variation during combustion, we need to consider the energy released from the breaking and forming of bonds. Given the energy values provided in the question, we can calculate the enthalpy variation using the given equations:
Enthalpy variation = (Number of moles of C-C bonds broken * Energy of C-C bond)
+ (Number of moles of C-H bonds broken * Energy of C-H bond)
- (Number of moles of O-H bonds formed * Energy of O-H bond)
- (Number of moles of C-O bonds formed * Energy of C-O bond)
From the given information, petrol is composed of octane (C8H18). Therefore, we need to determine the number of C-C and C-H bonds broken and the number of O-H and C=O bonds formed during combustion.
C-C bonds in octane = 8
C-H bonds in octane = 18
O-H bonds formed = 4 (since octane has 4 hydrogen atoms attached to oxygen)
Plugging in the energy values and bond counts, we can calculate the enthalpy variation:
Enthalpy variation = (8 * 83 kcal) + (18 * 99 kcal) - (4 * 111 kcal) - (8 * 0 kcal)
= 664 kcal + 1782 kcal - 444 kcal - 0 kcal
= 3002 kcal
Therefore, the estimated enthalpy variation when burning 28.5 liters of petrol is 3002 kcal.