Activation energy and catalysts.

Step 1 of 5

The barrier

Carbon monoxide, $\mathrm{CO}$⁠, is a poisonous gas that comes out of an engine. With oxygen it can become carbon dioxide: $\mathrm{2CO + O_2 \rightarrow 2CO_2}$⁠. The reaction gives out a lot of energy, and yet in the flask, at 550 K and without a catalyst, almost nothing happens.

The top chart is the spread of energies from the last Lesson; the bottom chart is the reaction’s energy profile: the substances’ energy along the way from reactants to products.

Step 2 of 5

Putting in the platinum

A catalyst is a substance that speeds up a reaction without being used up by it. In a car’s catalytic converter the catalyst is platinum, a precious metal, in a thin layer over a large surface. Here Temperature is fixed at 550 K, the heat of an engine that has warmed up. Predict what Platinum catalyst will do.

Step 3 of 5

A lower hump

On the platinum the reaction goes another way: $\mathrm{O_2}$⁠ molecules bind to the metal and split into atoms, and $\mathrm{CO}$⁠ molecules landing beside them react with them. Each step on this route has a low barrier. On the energy profile this route is drawn as a dashed line.

Step 4 of 5

Heating instead

If the high barrier is the problem, could you just heat more? The last Lesson showed that heating grows the share that clears the barrier. Predict by how much.

Step 5 of 5

It never runs out

A catalyst takes part in the reaction, but does not appear in its overall equation: it comes out as it went in. Watch the plate at the bottom of the flask while the reaction runs.