The reaction of Fe2O3(s) with Al(s) to form Al2O3(s) and Fe(s) is...

Question

The reaction of Fe2O3(s) with Al(s) to form Al2O3(s) and Fe(s) is
called the thermite reaction and is highly exothermic. What role
does lattice energy play in the exothermicity of the reaction?

Accepted Answer

Welcome back everyone in this example, we're told that magnesium has the ability to reduce some metal oxides. However, the reaction of solid magnesium with solid zinc oxide is very endo thermic and produces solid magnesium oxide and solid zinc. We need to use lattice energy to explain why this reaction is endo thermic. So according to our prompt we have the reaction between magnesium and zinc oxide. These are both solids. And as a product we're going to produce magnesium oxide, solid and solid zinc. And sorry about that. So we should recall that lattice energy is describing the amount of energy required for one mole of our solid ionic compound in this case our product magnesium oxide to break up into its constituent ions. And we can find this amount of energy for our product magnesium oxide, the ionic compound here in our textbooks or online. So when we look up our lattice energy which is represented as delta H lattice for first magnesium oxide, we're going to see that it has a value and we'll put an equal sign, two negative 3795 kg joules per mole. On the other hand, we have our other ionic compound in our reaction being our zinc oxide solid here. And we should recognize that in our textbooks or online we find a lattice energy for our zinc oxide equal to a value of negative 4142 kg jewels per. Now, as we stated earlier, our lattice energy describes the amount of energy for our ionic compound to break into its constituent ionic parts. And so because we see that we have a more negative lattice energy value for our zinc oxide, That means, and we'll write that down more negative. That means that this compound is going to be more stable or has a more stable crystal lattice, which is just our arrangement of our molecules of zinc oxide arranged in a crystal. And so because we understand that our zinc oxide has the more stable crystal lattice, we would say that therefore our magnesium oxide has a less stable crystal lattice. And so thus energy is needed to compensate for that difference in our lattice energies of our magnesium oxide and zinc oxide. And if we recall what the definition of an endo thermic reaction is, we would recall that energy is needed in endo thermic reactions by react ints and is absorbed from the surroundings, usually as heat. And as we can see, there's a similar need for energy from the surroundings when it comes to magnesium oxides crystal lattice, since it's less stable as we stated. And so that is why this explains as to why our reaction is endo thermic. And so for our final answer, we're going to highlight the fact that we stated magnesium or zinc oxides crystal lattice is more stable because it's more negative or because it has a more negative lattice energy. And we would say that on the contrary therefore magnesium oxide has a less stable crystal lattice. And so energy is needed, which signals that we do have a endo thermic reaction. Since we understand that endo thermic reactions also require energy from the surroundings. And so what's highlighted in yellow would be our final answer explaining our endo thermic reaction. So I hope that everything I reviewed was clear. If you have any questions, please leave them down below, and I will see everyone in the next practice video.

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