00:02
In this question we are given this exothermic reaction.
00:06
We know that it is exothermic because we are told that the delta h for this reaction is negative.
00:12
So by definition a negative delta h for a reaction tells us it is exothermic.
00:18
So it's negative 847 .6 and that is kilojoules per mole of the reaction.
00:29
So as we look at this reaction we see the coefficients in the balanced equation show us that we need 2 moles of aluminum for every 1 mole of the iron 3 oxide to give us 2 moles of the iron and 1 mole of the aluminum oxide.
00:51
And this mole ratio just comes from the coefficients in this equation.
00:55
When there is no coefficient written it is understood that it is a 1.
00:59
So what we know is that energy wise we get negative 847 .6 kilojoules released for every mole of the reaction.
01:15
But looking at that reaction that is going to be for 2 moles of aluminum.
01:22
So we get negative 847 .6 kilojoules for every 2 moles of aluminum.
01:27
And we want to know if we start with 35 grams of aluminum how much heat is going to be released.
01:34
Well if we can convert from grams of aluminum to moles then we can convert to amount of energy and we can do that because we know the molar mass of aluminum.
01:46
For every mole of aluminum the periodic table tells us that its mass is going to be 26 .98 grams.
01:55
Okay so starting with what we are given that is 35 grams of aluminum.
01:59
35 .0 to be exact because we do want to keep our significant figures...