Calculate ∆H°rxn for the following reaction at 298 K.
SiH4(g) + 2O2(g) SiO2(g) + 2H2O(l)
dHo rxn = (n*dHo products) - (n*dHo reactants)
Look up the dHo values in your table (text, notes,web) and turn the crank. Post your work if you get stuck.
To calculate the enthalpy change (∆H°rxn) for a reaction, you can use standard enthalpy of formation (∆H°f) values. The formula for ∆H°rxn is:
∆H°rxn = Σ∆H°f (products) - Σ∆H°f (reactants)
Given that you want to calculate ∆H°rxn for the reaction:
SiH4(g) + 2O2(g) -> SiO2(g) + 2H2O(l)
Let's assign the ∆H°f values for each species as follows:
∆H°f(SiH4) = +32.4 kJ/mol
∆H°f(O2) = 0 kJ/mol (because it's an element in its standard state)
∆H°f(SiO2) = -910.9 kJ/mol
∆H°f(H2O) = -285.8 kJ/mol
Now, you can substitute the values into the ∆H°rxn formula:
∆H°rxn = [∆H°f(SiO2) + 2∆H°f(H2O)] - [∆H°f(SiH4) + 2∆H°f(O2)]
∆H°rxn = [(-910.9 kJ/mol) + 2(-285.8 kJ/mol)] - [32.4 kJ/mol + 2(0 kJ/mol)]
Simplifying the equation:
∆H°rxn = -1482.5 kJ/mol - 32.4 kJ/mol
∆H°rxn = -1514.9 kJ/mol
Therefore, the enthalpy change (∆H°rxn) for the given reaction at 298 K is approximately -1514.9 kJ/mol.
To calculate ∆H°rxn, which is the standard enthalpy change for a reaction, you need to use standard enthalpy of formation values (∆H°f) for each compound involved in the reaction.
Here's how to proceed:
1. Look up the standard enthalpy of formation values (∆H°f) for SiH4(g), O2(g), SiO2(g), and H2O(l).
2. Write the balanced chemical equation for the reaction: SiH4(g) + 2O2(g) → SiO2(g) + 2H2O(l)
3. Determine the stoichiometric coefficients in the balanced equation.
- SiH4(g) appears as 1 on the left side of the equation.
- O2(g) appears as 2 on the left side and right side of the equation.
- SiO2(g) appears as 1 on the right side of the equation.
- H2O(l) appears as 2 on the right side of the equation.
4. Calculate the ∆H°rxn using the ∆H°f values and stoichiometric coefficients of each compound:
∆H°rxn = (∆H°f(SiO2(g)) + 2∆H°f(H2O(l))) - (∆H°f(SiH4(g)) + 2∆H°f(O2(g)))
5. Substitute the values from step 4 into the equation and perform the calculation.
6. Make sure to use consistent units for the ∆H°f values (usually in kJ/mol).
7. The resulting value will be the ∆H°rxn for the given reaction at 298 K.