Calculate the heat of formation reaction for
SiO2(s)+4HF(g) --> SiF4(g)+2H2O(l)
I got -129.6 and it says I'm wrong
You didn't show your work. I ran through it very quickly and I could have made a math error but I ended up with -103.7.
To calculate the heat of formation reaction for a given chemical equation, you need to know the standard heats of formation for each compound involved in the reaction. The standard heat of formation (ΔHf) is the change in enthalpy that occurs when one mole of a compound is formed from its elements in their standard states.
Using the given equation:
SiO2(s) + 4HF(g) → SiF4(g) + 2H2O(l)
The standard heats of formation for SiO2(s), HF(g), SiF4(g), and H2O(l) are as follows:
ΔHf(SiO2) = -910.9 kJ/mol
ΔHf(HF) = -272.3 kJ/mol
ΔHf(SiF4) = -1618.7 kJ/mol
ΔHf(H2O) = -285.8 kJ/mol
To calculate the heat of formation reaction, you can use the following equation:
ΔH = ΣΔHf(products) - ΣΔHf(reactants)
Plugging in the values:
ΔH = [ΔHf(SiF4) + 2ΔHf(H2O)] - [ΔHf(SiO2) + 4ΔHf(HF)]
ΔH = [-1618.7 kJ/mol + 2(-285.8 kJ/mol)] - [-910.9 kJ/mol + 4(-272.3 kJ/mol)]
ΔH = -1618.7 kJ/mol - 571.6 kJ/mol + 910.9 kJ/mol + 1089.2 kJ/mol
ΔH = -90.2 kJ/mol
Therefore, the correct heat of formation reaction for the given equation is -90.2 kJ/mol, not -129.6 kJ/mol.
To calculate the heat of formation (ΔHf) for a reaction, you need to use the standard heat of formation values for each compound involved in the reaction. These values represent the amount of heat absorbed or released when one mole of a compound is formed from its elements, with all substances in their standard states at a given temperature (usually 25°C or 298 K).
To obtain the correct answer, you'll need to know the standard heat of formation values for SiO2(s), HF(g), SiF4(g), and H2O(l). Here are the values:
ΔHf(SiO2(s)) = -910.9 kJ/mol
ΔHf(HF(g)) = -271.0 kJ/mol
ΔHf(SiF4(g)) = -1615.3 kJ/mol
ΔHf(H2O(l)) = -285.8 kJ/mol
Next, you'll need to use the stoichiometric coefficients in the balanced equation to calculate ΔHf for the given reaction.
SiO2(s) + 4HF(g) → SiF4(g) + 2H2O(l)
Using these coefficients, the ΔHf for the reaction can be calculated as follows:
ΔHf = [(nΔHf products) - (nΔHf reactants)]
ΔHf = [(1 mol × ΔHf(SiF4(g))) + (2 mol × ΔHf(H2O(l)))] - [(1 mol × ΔHf(SiO2(s))) + (4 mol × ΔHf(HF(g)))]
Substituting the values:
ΔHf = [(1 mol × -1615.3 kJ/mol) + (2 mol × -285.8 kJ/mol)] - [(1 mol × -910.9 kJ/mol) + (4 mol × -271.0 kJ/mol)]
ΔHf = (-1615.3 kJ/mol - 571.6 kJ/mol) - (-910.9 kJ/mol - 1084.0 kJ/mol)
ΔHf = -2186.9 kJ/mol + 1994.9 kJ/mol
ΔHf = -192.0 kJ/mol
Therefore, the heat of formation for the given reaction is -192.0 kJ/mol.