I/GCSE Chemistry Question Analysis Topic: Chapter 1: Principles of Chemistry - Chemical Formulae (Part 1)
For I/GCSE Chemistry, you should know:
A crucial sub-topic within this chapter is "Chemical Formulae, Equations, and Calculations." Let's dive in and explore this important aspect of chemical concepts.
Writing Word Equations and Balanced Chemical Equations:
When describing a chemical reaction, we can start by writing a word equation, which uses the full names of the reactants and products. For example, the word equation for the reaction between hydrogen gas and oxygen gas to form water would be:
Hydrogen + Oxygen → Water
To be more precise, we can then write a balanced chemical equation, which uses the chemical symbols and the correct stoichiometric coefficients to represent the reactants and products. The balanced equation for the same reaction would be:
2H₂ + O₂ → 2H₂O
The balanced equation shows that two molecules of hydrogen gas (2H₂) react with one molecule of oxygen gas (O₂) to produce two molecules of water (2H₂O).
Calculating Relative Formula Masses (RFM):
The relative formula mass (RFM), also known as the relative molecular mass (Mr), is the sum of the relative atomic masses of the atoms in a chemical formula. To calculate the RFM, we need to know the relative atomic masses (Ar) of the elements involved.
For example, to calculate the RFM of water (H₂O):
Relative atomic mass of hydrogen (Ar(H)) = 1.0
Relative atomic mass of oxygen (Ar(O)) = 16.0
RFM of H₂O = (2 × 1.0) + 16.0 = 18.0
The Mole: The Unit for Amount of Substance:
The mole (mol) is the unit used to measure the amount of a substance. One mole of a substance contains 6.022 × 10^23 particles (atoms, molecules, or ions), which is known as Avogadro's constant.
The number of moles (n) of a substance can be calculated using the following formula:
n = m / M
Where:
- n is the amount of substance in moles
- m is the mass of the substance in grams
- M is the relative formula mass (RFM) of the substance
Calculations Involving Amount of Substance, Relative Atomic Mass, and Relative Formula Mass:
Using the concepts of relative atomic mass, relative formula mass, and the mole, we can perform various calculations in chemistry. Here are some examples:
- Calculating the mass of a substance given the amount of substance in moles:
Mass (m) = Amount of substance (n) × Relative formula mass (M) - Calculating the amount of substance in moles given the mass and relative formula mass:
Amount of substance (n) = Mass (m) / Relative formula mass (M) - Determining the number of particles (atoms, molecules, or ions) in a given amount of substance:
Number of particles = Amount of substance (n) × Avogadro's number (6.022 × 10^23)
These calculations are essential for understanding stoichiometry, which is the quantitative relationship between the reactants and products in a chemical reaction.
Work hard for your I/GCSE Chemistry examination!
End of analysis. Great!
