Using the information provided calculate the heat of reaction involved in the conversion of 25.00 g of methane (CH4, MM=16.0426 g/mol) to chloroform (CHCl3, MM=119.3779 g/mol):
CH4(g) + 3 Cl2(g) --> CHCl3(l) + 3 HCl(g)
Given the following:
C(graphite) + 2 H2(g) --> CH4(g)
deltaH = -92.3 kJ
C(graphite) + 1/2 H2(g) + 3/2 Cl2(g) --> CHCl3(l)
dH = -74.5 kJ
1/2 H2(g) + 1/2 Cl2(g) --> HCl(g)
dH = -135.1 kJ
ANS:
-603.9 kJ
Much help is appreciated! Thank you!
Reverse equn 1 (and the sign of dH)
add in equn 2 as is.
Multiply eqn 3 by 3 and add in. Multiply the dH by 3 also.
You should have dH rxn of 92.3 - 74.5 - 3(-135.2) = -?
Then dHrxn x (25.0/molar mass CH4) = ?
Thank you very much!
To calculate the heat of reaction involved in the conversion of methane to chloroform, you need to use Hess's Law. Hess's Law states that the overall enthalpy change of a reaction is equal to the sum of the enthalpy changes of the individual steps of the reaction.
The given reaction is:
CH4(g) + 3 Cl2(g) --> CHCl3(l) + 3 HCl(g)
To calculate the heat of reaction, you need to use the enthalpy change values given for each step of the reaction. The steps are:
1. C(graphite) + 2 H2(g) --> CH4(g) (deltaH = -92.3 kJ)
2. C(graphite) + 1/2 H2(g) + 3/2 Cl2(g) --> CHCl3(l) (deltaH = -74.5 kJ)
3. 1/2 H2(g) + 1/2 Cl2(g) --> HCl(g) (deltaH = -135.1 kJ)
To calculate the overall heat of reaction, you need to add the enthalpy changes of the individual steps, making sure to account for any coefficient changes necessary to balance the equations.
The given reaction requires 1 mole of methane, so you need to convert the mass of methane to moles:
25.00 g CH4 * (1 mol CH4 / 16.0426 g CH4) = 1.5574 mol CH4
Now, let's calculate the overall heat of reaction:
Step 1: Since 1 mole of methane is produced in step 1, the enthalpy change for step 1 is multiplied by the number of moles of methane (1.5574).
Step 2: The enthalpy change of step 2 (-74.5 kJ) is already balanced, so no additional calculations are needed.
Step 3: The enthalpy change of step 3 (-135.1 kJ) needs to be multiplied by the number of moles of HCl produced in the reaction, which is 3 (according to the balanced equation).
Now, let's calculate the overall heat of reaction:
Overall heat of reaction = (deltaH1 * n1) + (deltaH2 * n2) + (deltaH3 * n3)
where deltaH1, deltaH2, and deltaH3 are the enthalpy changes of steps 1, 2, and 3 respectively, and n1, n2, and n3 are the coefficients in the balanced equation.
Overall heat of reaction = (-92.3 kJ * 1.5574) + (-74.5 kJ * 1) + (-135.1 kJ * 3)
Overall heat of reaction = -603.9 kJ
Therefore, the heat of reaction involved in the conversion of 25.00 g of methane to chloroform is -603.9 kJ.