C3 Chemical economics
- Created by: GraceLong
- Created on: 08-06-16 11:27
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- C3 Chemical economics
- Calculations and energy
- The relative atomic mass can be found on the periodic table and it can be used to calculate the molecular mass
- In all chemical equations, the total mass of the reactants is equal to the total mass of the products because atoms cannot be created or destroyed
- In chemical symbol equation, there are the same amount of atoms on each side. Predictions can be made by using the symbol equation as to how much of a reactant is needed to create a certain amount of product
- In practice, the amount of product is less because product is lost through some processes. Percentage yield is calculated by the actual yield over the predicted yield. Industrial processes need a high percentage yield to reduce the amount of reactants wasted and reduce their costs
- Atom economy is found by dividing the MR of the desired product over the sum of the MR of all the products. Industries what high atom economy because it reduces the production of unwanted products that need disposing of and they want to make the process more sustainable by making better use of the reactants
- Bond breaking at the start of reactions is endothermic. Bond making at the end of reactions is exothermic
- To find out the energy released by 1g of fuel, the fuel is measured into a spirit burner and heats water in a copper calorimeter. The temperature rise is then measured
- Allotropes of carbon
- Diamond, graphite and fullerenes are all allotropes of carbon which means they have different structures. Fullerenes are spheres are tubes and they are used to carry and deliver drugs to the body
- Diamond and graphite both are giant covalent structures. Diamond is the hardest substance known and it has a VERY high melting and boiling point. Graphite has a high melting and boiling point but layers can slide over each other
- Giant covalent bonding involves electron sharing and every carbon in diamond is bonded in a tetrahedral lattice. Every carbon in graphite is bonded in flat hexagonal layers which leaves unshared electrons on the outer shell
- Giant covalent bonding: high melting point, hard if bonds in different directions, easy to cut if bonds in layers, no free electrons so not conduct electricity. Nanotubes can be used in catalyst systems because atoms from catalyst only attracted to large surface area
- Rate of reaction
- Rate of reaction measures how much product is formed in a fixed period of time. The gradient of a graph can show the rate of reaction
- The limiting reactant is not in excess and it gets used up by the end of the reaction. The product produced is directly proportional to the limiting reactant
- Chemical reactions take places when particles collide. Therefore when temperature, concentration and pressure increase, the collision frequency increases and the rate of reaction increases
- For a successful collision, particles must have enough energy to react
- Combustible powders cause explosions because they have a large surface area . When some powders react with oxygen, a large volume of carbon dioxide is produced
- Catalysts change the rate of reaction and they are unchanged at the end of the reaction. Only small quantities of a catalyst are needed because the catalysts are specific to the reaction
- Batch or continuous?
- Continuous processes create large amounts of product constantly and they take place in a large plant with good transport links - there is minimum labour cost because plants are automated
- Batch processes are used for small quantities and they make a fixed amount. They can make batches which are then stored until needed and quantities have to be sold within a given time. Batch is easy to make a new batch when needed and it is easy to change production to a different product
- The disadvantages of continuous are that there is a high initial building coat and the process is inefficient is it has to be stopped. The disadvantages of batch are that they have to be supervised so labour cost is high and it is inefficient as the production is not in use all the time
- Medicines are expensive because they take ten years to develop and test and each country has different safety rules. Many compounds need to be made before a useful one is found and raw materials are often rare and expensive.
- Extracting chemicals from a plant involves: crushing to disrupt cell walls, boiling in a suitable solvent to dissolve compounds, chromatography to separate and identify individual compounds and isolating, purifying and testing potentially useful compounds
- Calculations and energy
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