WEBVTT

1
00:00:00.000 --> 00:00:05.979
Here is the problem: Balance the chemical equation Mg plus O2 → MgO.

2
00:00:06.429 --> 00:00:11.189
Balance atoms of every element, then use the coefficients as mole ratios.

3
00:00:11.989 --> 00:00:21.277
Write an atom balance for each element. Give each species an unknown coefficient; atoms of every element must be equal on both sides.

4
00:00:21.727 --> 00:00:31.630
Solve the linear system with the smallest whole numbers. Exact elimination leaves one free coefficient; scaling by the least common denominator gives integers.

5
00:00:32.080 --> 00:00:33.253
Balanced equation.

6
00:00:34.053 --> 00:00:38.442
So the answer is 2Mg plus O2 → 2MgO.

7
00:00:38.892 --> 00:00:56.307
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
00:00:57.107 --> 00:01:02.030
Mg: 2 equals 2, O: 2 equals 2, which checks out.