Question

the reaction of tetraphosphorus decaoxide with water to form phosphoric acid(aq) proceeds as follows: p4o10(s) + 6h2o(l) → 4h3po4(aq). when 80.9 grams of p4o10(s) react with sufficient h2o(l), 129 kj of energy are evolved. what is the value of δh for the chemical equation given? δh = kj

Explanation:

Step1: Calculate molar mass of $P_4O_{10}$

The molar mass of $P_4O_{10}$: $4\times30.97 + 10\times16.00=283.88\ g/mol$.

Step2: Calculate number of moles of $P_4O_{10}$

The number of moles of $P_4O_{10}$, $n=\frac{m}{M}=\frac{80.9\ g}{283.88\ g/mol}\approx0.285\ mol$.

Step3: Determine $\Delta H$

If 129 kJ of energy is evolved for 0.285 mol of $P_4O_{10}$, for 1 - mole of $P_4O_{10}$, $\Delta H=\frac{129\ kJ}{0.285\ mol}\times1\ mol\approx - 453\ kJ$ (negative because energy is evolved).

Answer:

• 453