The type of disposable hand warmer shown uses a chemical reaction of iron to generate heat - Leaving Cert Chemistry - Question b - 2016

If iron pellets were used instead of iron powder, the result would be that the reaction would take place more slowly. This is because pellets have a smaller surface area compared to the powder. A larger surface area allows for more collisions between reactants, leading to a faster reaction. Therefore, using powder would cause the hand warmer to heat up more quickly than if pellets were used.

To find the number of moles of iron, we can use the formula:

$n = \frac{m}{M}$

where:

• $m$ is the mass of iron (28 g)
• $M$ is the molar mass of iron, which is approximately 56 g/mol

Thus:

$n = \frac{28 ext{ g}}{56 ext{ g/mol}} = 0.5 ext{ moles}$

From the balanced equation:

$4Fe + 3O_2 \rightarrow 2Fe_2O_3$

We can determine the mole ratio:

$4 ext{ moles of Fe} \rightarrow 2 ext{ moles of Fe}_2O_3$

Thus, if we have 0.5 moles of Fe, we can set up a proportion to find the moles of Fe2O3 produced:

$\frac{4 ext{ moles Fe}}{2 ext{ moles Fe}_2O_3} = \frac{0.5}{x}$

Solving for $x$ gives:

$x = \frac{0.5 imes 2}{4} = 0.25 ext{ moles of Fe}_2O_3$