WEBVTT

1
00:00:00.000 --> 00:00:06.107
Here is the problem: Balance the chemical equation Al plus O2 → Al2O3.

2
00:00:06.557 --> 00:00:11.317
Balance atoms of every element, then use the coefficients as mole ratios.

3
00:00:12.117 --> 00:00:21.568
Write an atom balance for each element. Give each species an unknown coefficient; atoms of every element must be equal on both sides.

4
00:00:22.017 --> 00:00:31.990
Solve the linear system with the smallest whole numbers. Exact elimination leaves one free coefficient; scaling by the least common denominator gives integers.

5
00:00:32.440 --> 00:00:33.566
Balanced equation.

6
00:00:34.366 --> 00:00:40.125
So the answer is 4Al plus 3O2 → 2Al2O3.

7
00:00:40.574 --> 00:00:58.361
Coefficients in a balanced equation count particles (moles), not grams. Convert grams to moles, apply the mole ratio, then convert back to grams with the other species prime molar mass. Assumes the reaction goes to completion with the known species fully consumed (or formed).

8
00:00:59.161 --> 00:01:04.478
Al: 4 equals 4, O: 6 equals 6, which checks out.