How much heat is liberated from the complete combustion

[~angel~]

The complete combustion of RDX is 2C3H6N6O6 + 302 --> 6H2O + 6CO2 + 6N2.

How much heat is liberated from the complete combustion of 10g of RDX?

delta H values: H20 = -286, CO2 = -394, RDX = +65 (all in kJ/mol)

I thought it'll be (6*-286 + 6*-394) - (2*65)
= -4210 kJ/mol

Then divide that by the amount of moles in 100g. But I end up with this massive number which is wrong. I'm not sure whether to take into acount the 2 moles of RDX reacting when finding the amount of moles in 100g as well.

Thanks.

 

[vsage]

Why did you divide it when the units you found for $$\Delta H$$ implies you multiply by the number of moles? Also, remember the number you found is actually the heat liberated per *2* mol of RDX.

 

[thepatientmental]

Based on the given delta H values, the correct calculation for the heat liberated from the complete combustion of RDX is: (6*-286 + 6*-394) - (2*65) = -4210 kJ/mol. However, to find the heat liberated from the combustion of 10g of RDX, we need to convert the given delta H values from kJ/mol to kJ/g. This can be done by dividing each value by the molar mass of the substance in grams.

For H2O: -286 kJ/mol / 18 g/mol = -15.89 kJ/g
For CO2: -394 kJ/mol / 44 g/mol = -8.95 kJ/g
For RDX: 65 kJ/mol / 222 g/mol = 0.29 kJ/g

Next, we need to calculate the amount of moles in 10g of RDX. To do this, we divide the given mass by the molar mass of RDX: 10g / 222 g/mol = 0.045 moles.

Now, we can calculate the heat liberated from the combustion of 10g of RDX by multiplying the kJ/g values by the number of moles and the given coefficients in the balanced equation:

(6*-15.89 + 6*-8.95) - (2*0.29) * 0.045 moles = -0.71 kJ

Therefore, the heat liberated from the complete combustion of 10g of RDX is -0.71 kJ. It is important to note that this value is negative, indicating that the reaction is exothermic and releases heat. Also, it is not necessary to include the 2 moles of RDX in the calculation of the amount of moles in 10g, as they are already accounted for in the coefficients of the balanced equation.