chemical energetics and reactions

bonds break and new bonds form

they provide the energy for chemical reactions

the minimum amount of energy particles must collide with in order to break bonds

You need a collision to have a reaction. ​ Collisions provide the energy required to break bonds.​ Most collisions are not successful.​ A successful collision is very important for any chemical reaction.

reactants -> products + energy

energy + reactants -> products

• energy is released by reaction • energy level of reactants is higher than products • activation energy is achieved earlier (peaks earlier)

• energy is absorbed by reaction • energy level of reactants is lower than products • activation energy is achieved later (peaks later)

Increase in the concentration of a solution, the rate of reaction will increase This is because there will be more reactant particles in a given volume, allowing more frequent and successful collisions per second, increasing the rate of reaction

Increase in the surface area of the solid, the rate of reaction will increase This is because more surface area particles will be exposed to the other reactant so there will be more frequent and successful collisions per second, increasing the rate of reaction

Increase in the temperature, the rate of reaction will increase This is because the particles will have more kinetic energy than the required activation energy, therefore there will be more frequent and successful collisions per second, increasing the rate of reaction

Catalysts reduce the activation energy as they create alternative pathways requiring lower activation energy, allowing more successful and frequent collisions This shows that when a catalyst is used, the rate of reaction will increase

Explosive combustion occurs when there are many fine particles in the air Many industrial processes such as metal working, coal mining or flour milling produce very fine and tiny particles These particles have a very large surface area and are combustible in air Even a small spark may cause them to ignite and since the surface area is so large, the rate of reaction can be incredibly fast, hence they are explosive Methane gas mixed with air in coal mines can also form an explosive mixture

Method: Add dilute hydrochloric acid into a conical flask Use a capillary tube to connect this flask to a measuring cylinder upside down in a bucket of water (downwards displacement) Add calcium carbonate chips into the conical flask and close the bung Measure the volume of gas produced in a fixed time using the measuring cylinder Repeat with different sizes of calcium carbonate chips (solid, crushed and powdered) Result: Smaller sizes of chips causes an increase in the surface area of the solid, so the rate of reaction will increase This is because more surface area of the particles will be exposed to the other reactant so there will be more frequent and successful collisions, increasing the rate of reaction

Method: Measure 50 cm3 of Sodium Thiosulfate solution into a flask Measure 5 cm3 of dilute Hydrochloric acid into a measuring cylinder Draw a cross on a piece of paper and put it underneath the flask Add the acid into the flask and immediately start the stopwatch Look down at the cross from above and stop the stopwatch when the cross can no longer be seen Repeat using different concentrations of Sodium Thiosulfate solution (mix different volumes of sodium thiosulfate solution with water to dilute it) Result: With an increase in the concentration of a solution, the rate of reaction will increase This is because there will be more reactant particles in a given volume, allowing more frequent and successful collisions, increasing the rate of reaction

Method: Dilute Hydrochloric acid is heated to a set temperature using a water bath Add the dilute Hydrochloric acid into a conical flask Add a strip of Magnesium and start the stopwatch Stop the time when the Magnesium fully dissolves Repeat at different temperatures and compare results Result: With an increase in the temperature, the rate of reaction will increase This is because the particles will have more kinetic energy than the required activation energy, therefore more frequent and successful collisions will occur, increasing the rate of reaction

Compared to a reaction with a reactant at a low concentration, the graph line for the same reaction but at a higher concentration has a steeper gradient at the start and becomes horizontal sooner This shows that with increased concentration of a solution, the rate of reaction will increase

Compared to a reaction with lumps of reactant, the graph line for the same reaction but with powdered reactant has a steeper gradient at the start and becomes horizontal sooner This shows that with increased surface area of the solid, the rate of reaction will increase

The diagram shows that when a catalyst is used, the activation energy is reduced as it creates an alternative pathway requiring lower activation energy, allowing more successful and frequent collisions This shows that when a catalyst is used, the rate of reaction will increase

Compared to a reaction at a low temperature, the graph line for the same reaction but at a higher temperature has a steeper gradient at the start and becomes horizontal sooner This shows that with increased temperature, the rate of reaction will increase

Light wave energy (UV or Radiation = α,β,γ)acts as electromagnetic waves considered as an energy ‘bullets’ called photons ​ have sufficient energy to overcome the activation energy to break chemical bonds. greater the intensity of light , the more reactant molecules are likely to gain the required energy (activation energy) - reaction speed increases.​ not a catalyst - the photons of energy are used up in the chemical changes they induce, the photons cannot be recycled

Requires the input of sunlight energy and the green chlorophyll molecules absorb the photon energy packets of light and initiate the chemical changes. > Intensity Of Light, > Rate Of Photosynthesis. Factors affecting the rate - light, temperature & CO2 concentration

Each silver halide (AgCl, AgBr, AgI) salt has a different sensitivity to light (photosensitive).​ All three are used in the production of various types of photographic film to detect visible light and beta and gamma radiation from radioactive materials. AgI is the least sensitive and used in X-ray radiography, AgCl is the most sensitive and used in ‘fast’ film for cameras.

When radiation hits the film the silver ions in the salt are reduced by electron gain to silver​: Ag+ + e- → Ag​ Halide ion is oxidized to the halogen molecule by electron loss​: 2X- → X2 + 2e- (X = halogen atom, Cl, Br or I)​ Balance Equation : 2AgX → 2Ag + X2