How to Teach Gas Law Math
Do your students set up gas laws correctly, but make careless math errors?
Or worse-their math skills fall out of their brains as soon as they walk through your math-skill sucking doorway?
It's too bad. You'll have to tell your students that this condition is fatal to their grades. Plus, the only cure is to turn chemistry class into math class a few times. Tell students, “It’ll only sting a little at first.”
Then all those years of math will climb right back into their brains. And their grades will make a full recovery.
But seriously, lets turn your chemistry class into a math lab for a day.
How We Teach Gas Laws
Have students start by identifying and color coding the variables. Then have them plug the numbers into the color coded equation. Next have them solve the math by dividing both sides by the number next to the variable.
(I know this sounds ridiculously specific, but you must be this specific with your students. Remember all their math skills have fallen out of their heads. Funny, but true.)
Last, show the answer.
Then remind students to go back and check their work. Ask them if they see anything that might have been forgotten. If you are lucky, some student will say, “Sig figs.”
The key to making this stick is explaining and writing down the steps for students.
Do not do all the work in one step. You should feel like you rewrote the same thing 876 times.
Simplify Charles’ Law By Explaining Two Problem Types
Students hate fractions. There's no cure for that. It's a learn to live with it thing.
Which is why there are two examples that are essential to showing students Charles' Law:
One where you solve for volume (numerator variable) and one where you solve for temperature (denominator variable).
And the second one is much more fatal to students’ grades.
When you show students the first example the variable is in the numerator. All students need to do is to multiply each side of the equation by the number below the variable.
Tell students the reason we do that is to get the variable by itself.
Next have students rewrite the problem with all the numbers equal to the variable. Then have students do the math. Last, ask if we forgot anything. Hopefully, they learned from last time and the whole class suggests checking sig figs.
It also helps to tell students that they don’t need to show all of these steps. But they need to take down the steps and explain each step on a different line. Remind them that it might seem easy now, but at 10PM after ball practice, it will be 100 times easier with detailed notes.
Students have issues come up when the variable is in the denominator. They panic and surrender their grades to their failing fate.
But, walk them through this process, and it should calm their nerves.
Have students write down the equation again, but this time after they plug in the variables, students will see the variable in the denominator. Let them know the steps are different when the variable is in the bottom.
You’ll almost see the light bulbs going off above their heads. It’s great.
Tell them to multiply the left and right sides by the variable in the denominator. Then have them multiply both sides by the number next to the variable.
Last they do the math and ask them to check sig figs.
Now they solve the problem.
The Thing About Gay-Lussac’s Law
Gay-Lussac's Law is going to be the same math as Charles' Law. Explain that the math is going to be exactly the same.
There will be two problem types. Type 1 that has a variable in the numerator. And a type 2 that has the variable in the denominator.
As long as they identify where the variable is correctly, they will be able to set the problem up and solve it using the same steps as provided in the Charles’ Law examples.
Then for the sake of time move on to the ideal gas law.
Make the Ideal Gas Law Fun to Teach
Just like in the other laws, start by color coding (or labeling) the equation. Then have students plug the numbers into the color coded equation.
Again, make sure you are showing and having students write each step on a different line.
Then ask students where the variable is. They should tell you something like “on the right side.”
On a new line have them copy down and divide the number(s) next to the variable.
Next have students solve the math using their calculator. But, the biggest hang up might still be remembering significant figures.
It still feels awkward to do all that math only to round to 500. Tell students you feel the same way.
But the truth remains the same. Following and writing out all these rules is how we revive all those skills they lose when they cross the threshold into chemistry class.
After teaching these math lessons, have students try doodle notes. They go over the inverse and direct relationships and math word problems.
You and I love chemistry so we obviously want to be chemistry teachers. But, our students want to compartmentalize each class. We must really push hard about having strong math skills.
Color coding and having detailed explanations will help your students recover from ailing grades.