WEBVTT

1
00:00:00.000 --> 00:00:06.397
Here is the problem: Balance the chemical equation H2 plus O2 → H2O.

2
00:00:06.847 --> 00:00:11.688
Balance atoms of every element, then use the coefficients as mole ratios.

3
00:00:12.488 --> 00:00:21.497
Write an atom balance for each element. Give each species an unknown coefficient; atoms of every element must be equal on both sides.

4
00:00:21.947 --> 00:00:31.850
Solve the linear system with the smallest whole numbers. Exact elimination leaves one free coefficient; scaling by the least common denominator gives integers.

5
00:00:32.300 --> 00:00:33.438
Balanced equation.

6
00:00:34.238 --> 00:00:39.288
So the answer is 2H2 plus O2 → 2H2O.

7
00:00:39.738 --> 00:00:56.828
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
00:00:57.628 --> 00:01:02.945
H: 4 equals 4, O: 2 equals 2, which checks out.