Answer:
ΔH = -976.5 kJ
Explanation:
For the reaction given, there are 2 moles of benzene (C6H6). The heat of this reaction is -6278 kJ, which means that the combustion of 2 moles of benzene will lose 6278 kJ of heat. It is an exothermic reaction.
The value of ΔH, the enthalpy, is a way of measurement of the heat, and it depends on the quantity of the matter (number of moles).
So, 24.3 g of benzene has :
n = mass/ molar mass
n = 24.3/78.11
n = 0.311 moles
2 moles ------------ -6278 kJ
0.311 moles ----------- x
By a simple direct three rule:
2x = -1953.08
x = -976.5 kJ
Taking into account the definition of enthalpy of a chemical reaction, the quantity of heat released from the combustion of 24.3 g benzene is 976.229 kJ.
The enthalpy of a chemical reaction as the heat absorbed or released in a chemical reaction when it occurs at constant pressure. That is, the heat of reaction is the energy that is released or absorbed when chemicals are transformed into a chemical reaction.
The enthalpy is an extensive property, that is, it depends on the amount of matter present.
Amount of heat produced in this case
In this case, the balanced reaction is:
2 C₆H₆ + 15 O₂ → 12 CO₂ + 6 H₂O
and the enthalpy reaction ∆H° has a value of -6278 kJ.
This equation indicates that when 2 moles of C₆H₆ reacts with 15 moles of O₂, 6278 kJ of heat is released.
You need to know the amount of heat produced from the combustion of 24.3 g benzene (C₆H₆). Knowing that the molar mass of benzene is 78.11 g/mole, the number of moles of benzene reacting in the combustion is:
[tex]24.3 grams\frac{1 mole}{78.11 grams}[/tex]= 0.311 moles
So, when 0.311 moles of benzene are burned, then you can apply the following rule of three: if 2 moles of C₆H₆ releases 6278 kJ of heat, 0.311 moles of C₆H₆ releases how much heat?
[tex]heat=\frac{0.311 moles x6278 kJ}{2 moles}[/tex]
heat= 976.229 kJ
Finally, the quantity of heat released from the combustion of 24.3 g benzene is 976.229 kJ.
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