Rate of Reaction
Rate of reaction = mass of a product formed per second/minute/etc.
Limiting reactant = the reactant not in excess which is used up by the end of the reaction. The amount of product produced is directly proportional to the amount of limiting reactant used.
Reactions take place when particles collide successfully.
The rate of reaction depends on the number of successful collisions: more collisions = faster reaction.
The rate of reaction can be increased by:
- increasing temperature (giving particles more kinetic energy)
- increasing concentration (increases collision frequency as there is less space)
For a successful collision, particles must have enough energy to react.
Rate of Reaction (continued)
Increased surface area = increased rate of reaction.
When there is a large surface area, there are more particles exposed for reactions to happen.
Catalyst = speeds up the reaction, but remains unchanged at the end.
Each catalyst is specific to a certain reaction.
Relative Formula Mass = the largest number for each element shown on the periodic table.
Total mass of reactants = total mass of products.
Percentage yield = actual yield/predicted yield x 100%
Atom economy = Mass of desired products/mass of all products x 100%
Bond breaking is an endothermic process. Energy is taken from the surroundings to activate the reaction.
Bond making is an exothermic reaction. Energy is released into the surroundings when bonds are made.
If more energy is needed than released, the reaction is endothermic.
If more energy is released than needed, the reaction is exothermic.
Energy transferred (J) = mass x specific heat capacity x temperature change
Energy per gram = energy released (J)/mass of fuel burnt (g)
Continuous processing: highly automated, minimal labour costs, less energy to maintain. eg.ammonia, sulphuric acid. Inefficient when not in constant use, high set-up cost.
Batch processing: fixed amount, made when needed, 'sell by' date, easy to change production. eg.pharmaceuticals. Labour intensive and costly, long time to clean for product change, inefficient.
Drug development can be really expensive because:
- It takes 10 years to develop (staffing costs).
- Many different compounds need to be tested.
- Raw plant materials are difficult to extract, expensive and rare.
- Chromotography is used to separate and isolate potentially useful compunds.
- Products need to be tested on humans.
Allotropes and Nanochemistry
Allotropes = different structural forms of the same element.
Some allotropes of carbon are diamond, graphite and buckminsterfullerene.
Fullerenes can be used to carry and deliver drug molecules around the body or remove dangerous substances from the body. Buckminsterfullerene is made up of 60 carbon atoms in a sphere and each spere is 10^-9m long.
The carbon atoms in diamond each have a bond to another carbon atom in a giant covalent structure. As a result it has a very high melting/boiling point. As every atom shares an electron with 4 others, there are no free electrons and diamond does not conduct electricity.
Graphite has a high melting/boiling point, but the layers are allowed to slide over eachother, so it can be used as a lubricant. Each carbon atom is covalently bonded to three others, so there is a delocalised electron which is free to move, allowing graphite to conduct electricity.