Equilibrium: common misconceptions

If your child says… “The level stays still, so the molecules have stopped.”

Ask together

Could equal amounts leave and return without changing the level?

What’s true

An unchanged appearance cannot show whether molecules are moving.

If your child says… “Both solids need concentration terms too.”

Ask together

Would adding another lump change the concentration within a pure solid?

What’s true

Pure-solid factors are absorbed into the constant, which depends on temperature.

If your child says… “A large equilibrium constant means a fast reaction.”

Ask together

Where does this calculation tell us how long the reaction takes?

What’s true

The constant describes equilibrium composition, while speed also depends on energy barriers.

If your child says… “Removing gas should push the reaction back towards dissolved gas.”

Ask together

Which change would replace the gas that escaped?

What’s true

Removing carbon dioxide above the drink favours its replacement from the liquid.

If your child says… “Neutral water always has pH seven.”

Ask together

If warming increases both concentrations equally, does either become more abundant than the other?

What’s true

Neutrality requires equal hydronium and hydroxide concentrations; the corresponding pH depends on temperature.

If your child says… “Adding acetate makes more acid molecules split into ions.”

Ask together

Which direction uses up some of the added acetate?

What’s true

An added product ion favours the reverse change.

If your child says… “A buffer keeps its pH unchanged however much acid I add.”

Ask together

What happens when repeated acid additions use up the available acetate?

What’s true

A buffer has a limited supply of proton-accepting and proton-donating components.

If your child says… “A solid forms when the ion product is below the saturation value.”

Ask together

Would removing dissolved ions into a solid lower their product or raise it?

What’s true

Precipitation is favoured when the current ion product exceeds the saturation value.