Unit 4
Reactions and equations.
Atoms are never made or lost: conservation of mass, balanced equations, reacting masses, the limiting reagent and the yield.
Before this unit
- Bonding and structure
- The mole
- Linear equations Mathematics
The unit, lesson by lesson
Lessons
4 lessons · 21 practice questions · about 2 hours
Conservation of mass
What happens to atoms in a chemical reaction: they change partners and none is lost, so in a sealed vessel the mass does not change. And why a candle gets lighter as it burns.
Balancing equations
How to write a chemical reaction so that every atom is counted: coefficients in front of formulas, formulas you never change, elements that come in pairs, and a check by counting atoms.
Reacting masses
From a balanced equation to grams: relative molecular mass, the fixed ratio by mass between reactants, and the three steps from grams to moles, through the coefficients, and back to grams.
Limiting reagent and yield
Which runs out first and what is left in excess, why more of one reactant does not always give more product, and how to compare what you got in the lab with what you should have got.