Question

What mass of HF must react to produce 345 kJ of energy? Assume excess Sio2 sio2(s) + 4 HF(g) ? SiF4(g) + 2H20(,) 4Hxn--184 kJ

Answer 1

Answer: The mass of HF reacted is 150 g.

Explanation:

We are given:

Amount of energy released = -345 kJ

For the given chemical reaction:

$SiO_2(s)+4HF(g)\rightarrow SiF_4(g)+2H_2O(l);\Delta H_{rxn}=-184kJ$

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 = $\frac{4}{184}\times 345=7.5mol$ of hydrofluoric gas is reacted.

Now, to calculate the mass of HF, we use the equation:

$\text{Number of moles}=\frac{\text{Given mass}}{\text{Molar mass}}$

Molar mass of HF = 20 g/mol

Moles of HF = 7.5 moles

Putting values in above equation, we get:

$7.5mol=\frac{\text{Mass of HF}}{20g/mol}\\\\\text{Mass of HF}=150g$

Hence, the mass of HF reacted is 150 g.