00:01
Okay, so here elemental aluminum is produced when 79 grams of chromium reacts with excess aluminum oxide.
00:09
And so the balanced equation for this is al2 -03 combines with two chromium ones and goes to make elemental, or goes to make chromium oxide and elemental aluminum.
00:40
And so here we know that the delta h is 536.
00:48
Kilojoules.
00:50
And so the delta h here is positive, which means that this reaction is endothermic.
00:55
That means that the reaction is absorbing heat from the environment.
00:59
And so when something is endothermic, heat actually acts as one of the reactives, because the reaction won't occur without that heat present.
01:07
So we can actually write this like this.
01:10
So 536 kilojoules can become part of the balanced equation.
01:15
So a, we want to know what is happening to the temperature in the surroundings when this reaction occurs.
01:21
Well, because this reaction is taking heat from the surrounding area and putting it into this reaction, it's going to get colder because it's absorbing heat.
01:36
For b, we want to know how much heat would be needed for the 79 grams of chromium to react.
01:42
So here we can kind of do it like a normal using your balanced equation or dukeometry kind of problem.
01:52
Because 536 kilojoules is part of the balanced equation.
01:56
So we have 79 grams of chromium, and what we do is that whenever we're working with one of these balanced equations, we always convert into moles first.
02:06
So to convert into moles of chromium, we'll use the molar mass.
02:14
So one mole of chromium is 51 .96 grams.
02:34
So now we have moles of chromium, but we want to know the amount of heat needed.
02:39
So this is where the balanced equation comes in...