Separate chemistry 1 Revision Notes

What is Atom Economy?

Atom economy quantifies the proportion of reactant atoms that become part of the desired product in a chemical reaction. It's an important metric for assessing the sustainability and efficiency of chemical processes. The higher the atom economy, the less waste is generated, making the process more 'green'.

Calculating Atom Economy

To calculate atom economy, use the formula: (Relative formula mass of desired product / Relative formula mass of all reactants) × 100%. Remember to consider the stoichiometry of the reaction when calculating the total relative formula mass of reactants and products. Always aim for 100% atom economy to prevent waste.

Importance of High Atom Economy

Reactions with high atom economy are desirable because they produce less waste, which reduces disposal costs and environmental impact. This also means that fewer raw materials are consumed for the same amount of desired product, leading to more efficient resource utilisation and lower production costs for industries.

Key Data in Pathway Choice

Chemists compare atom economy (the proportion of reactant atoms that become the main product), percentage yield (the ratio of actual to theoretical product made), reaction rate (how fast the reaction occurs), equilibrium position (the extent to which products are formed at equilibrium under industrial conditions), and whether by-products are valuable or need costly disposal. These criteria help in evaluating the economic, environmental and practical suitability of each pathway.

Calculating Atom Economy and Yield

Atom economy is calculated as (Mr of desired product ÷ sum of Mr of all reactants, from the balanced equation) × 100%. This shows the efficiency of turning raw materials into useful output, especially in reactions with multiple products. Percentage yield is (actual mass of product ÷ theoretical mass from balanced equation) × 100%. Both calculations are key in selecting efficient, cost-effective, and sustainable processes.

Environmental and Practical Considerations

Other important factors include the source of raw materials (renewable or non-renewable), energy requirements, waste production, and the hazards of reactants and by-products. Even if a pathway is not the most efficient in terms of yield, it may be preferred if it uses greener materials, produces less hazardous waste, or generates useful by-products.

Defining Molar Volume

Molar volume is the volume that one mole of any gas occupies. This definition holds true for any gas, regardless of its chemical identity, at a constant temperature and pressure. It's a fundamental concept in gas chemistry.

Molar Volume at Room Temperature and Pressure (RTP)

At room temperature and pressure, the molar volume of any gas is accepted to be 24 dm³ or 24,000 cm³. This constant value simplifies calculations involving gases, allowing direct conversion between moles and volume without needing the individual gas's molar mass.

Importance in Calculations

Understanding molar volume is essential for calculating the volume of a gas from a given number of moles, or vice versa. It links the amount of substance (in moles) to the physical space it occupies, which is vital for understanding chemical reactions involving gaseous reactants or products.

Understanding Molar Volume

The molar volume is the volume occupied by one mole of any gas at a specific temperature and pressure. At room temperature and pressure (r.t.p.), which is approximately 20°C and 1 atmosphere (or 101 kPa), one mole of any gas occupies 24 dm³ (24,000 cm³). This generalisation is highly useful for calculations involving gases in chemical reactions.

Using Balanced Equations in Calculations

Balanced chemical equations provide the molar ratios between reactants and products. To calculate the volume of a gas from the mass of a solid (or vice versa), first convert the given mass to moles using the molar mass. Then, use the stoichiometric ratio from the balanced equation to find the moles of the gas. Finally, convert moles of gas to volume using the molar volume (24 dm³ per mole at r.t.p.).

Steps for Gas Volume Calculations

1. Write and balance the chemical equation. 2. Convert known masses (or volumes, if starting with a liquid/solution) to moles using molar mass (or concentration). 3. Use the molar ratios from the balanced equation to find the moles of the unknown gas. 4. Convert moles of gas to volume using the molar volume (volume = moles × 24 dm³ at r.t.p.). Remember to ensure all units are consistent (e.g., cm³ or dm³).