Answer: The mass of HF reacted is 150 g.
Explanation:
We are given:
Amount of energy released = -345 kJ
For the given chemical reaction:
[tex]SiO_2(s)+4HF(g)\rightarrow SiF_4(g)+2H_2O(l);\Delta H_{rxn}=-184kJ[/tex]
By Stoichiometry of the reaction:
184 kJ of energy is released when 4 moles of hydrofluoric gas is reacted.
So, 345 kJ kJ of energy will be released when = [tex]\frac{4}{184}\times 345=7.5mol[/tex] of hydrofluoric gas is reacted.
Now, to calculate the mass of HF, we use the equation:
[tex]\text{Number of moles}=\frac{\text{Given mass}}{\text{Molar mass}}[/tex]
Molar mass of HF = 20 g/mol
Moles of HF = 7.5 moles
Putting values in above equation, we get:
[tex]7.5mol=\frac{\text{Mass of HF}}{20g/mol}\\\\\text{Mass of HF}=150g[/tex]
Hence, the mass of HF reacted is 150 g.
150 g of HF must react to produce 345 kJ of energy when reacting with SiO₂.
Let's consider the following thermochemical equation.
SiO₂(s) + 4 HF(g) ⇒ SiF₄(g) + 2 H₂O(l) ΔHrxn = -184 kJ
184 kJ of heat are evolved when 4 moles of HF react. The moles of HF that must react to release 345 kJ are:
[tex]-345kJ \times \frac{4mol}{(-184kJ)} = 7.50 mol[/tex]
We will convert 7.50 moles of HF to grams using its molar mass (20.01 g/mol).
[tex]7.50 mol \times \frac{20.01g}{mol} = 150 g[/tex]
150 g of HF must react to produce 345 kJ of energy when reacting with SiO₂.
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