CSEE (Form 4) Quantitative aspects of chemical change — practice questions

1. Chemists often need to know how many particles are present rather than what they weigh. 2. The amount of substance is so important that it is given its own name, the mole. 3. The mole is a counting unit, in the same way that a dozen or an hour is a counting unit. _Source: Siyavula Physical Sciences Grade 10 (Everything Science, CC BY 4.0), Chapter 19: Quantitative aspects of chemical change_

1. The number written in front of a substance in a balanced equation gives the mole ratio. 2. If no number is written, that number is taken to be one. 3. For the synthesis of ammonia the balanced equation carries a one, a three and a two. 4. One mole of nitrogen molecules reacts with three moles of hydrogen molecules. 5. Those two together produce two moles of ammonia molecules. 6. So three moles of hydrogen are needed for every one mole of nitrogen. 7. Answering two picks up the ammonia coefficient by mistake rather than the hydrogen one. _Source: Siyavula Physical Sciences Grade 10 (Everything Science, CC BY 4.0), Chapter 19: Quantitative aspects of chemical change_