Question

The thermite reaction, below, is highly exothermic. 2Al(s) + Fe₂O₃(s) ? 2Fe(s) + Al₂O₃(s), ΔH = -850 kJ What mass of iron is formed when 725 kJ of heat is released?

a) 47 g
b) 65 g
c) 95 g
d) 112 g
e) 130 g

Answer 1

It is not possible to form iron when 725 kJ of heat is released in the thermite reaction.

Step-by-step explanation:

The thermite reaction is highly exothermic and can be represented by the equation 2Al(s) + Fe₂O₃(s) --> 2Fe(s) + Al₂O₃(s). The enthalpy change, ΔH, for this reaction is -850 kJ. To determine the mass of iron formed when 725 kJ of heat is released, we first need to calculate the moles of heat released using the enthalpy change. This can be done by dividing the heat released (725 kJ) by the enthalpy change (-850 kJ) and then converting moles of heat to moles of iron using the stoichiometry of the reaction. Finally, we can calculate the mass of iron formed by multiplying the moles of iron by its molar mass.

First, let's calculate the moles of heat released:

1. Calculate the moles of heat released = Heat released (kJ) / Enthalpy change (kJ)
2. Convert the moles of heat to moles of iron using the stoichiometry of the reaction: 1 mol of Fe is formed for every 2 mol of heat released.

Now, let's calculate the mass of iron formed:

1. Calculate the moles of Fe formed = Moles of heat released / 2
2. Calculate the mass of Fe formed = Moles of Fe formed * Molar mass of Fe

Substituting the values:

1. Moles of heat released = 725 kJ / -850 kJ = -0.853 mol
2. Moles of Fe formed = -0.853 mol / 2 = -0.427 mol
3. Mass of Fe formed = -0.427 mol * 55.845 g/mol (molar mass of Fe) = -23.857 g