chemical energetics and reactions Flashcards
what happens in a chemical reaction
bonds break and new bonds form
what do collisions do in a chemical reaction
they provide the energy for chemical reactions
What is activation energy
the minimum amount of energy particles must collide with in order to break bonds
what is collision theory
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.
exothermic reaction equation
reactants -> products + energy
endothermic reaction equation
energy + reactants -> products
describe exothermic reactions
- energy is released by reaction
- energy level of reactants is higher than products
- activation energy is achieved earlier (peaks earlier)
describe endothermic reactions
- energy is absorbed by reaction
- energy level of reactants is lower than products
- activation energy is achieved later (peaks later)
how does concentration affect rate of reaction and why
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
how does surface area affect rate of reaction and why
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
how does temperature affect rate of reaction and why
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
how do catalysts affect rate of reaction and why
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
what is explosive combustion
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
investigation for surface area
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
investigation for concentration
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
investigation for temperature
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
graph for higher concentration
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
graph for particle size/surface area
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
graph for catalyst
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
graph for temperature
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
photochemical reactions + properties
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
photosynthesis characterisitc
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
photography characteristic
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.
equation for photography
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
what are NPK fertilisers
Fertilisers contain nitrogen, potassium and phosphorus
Nitrogen promotes healthy leaves, potassium promotes growth and healthy fruit and flowers and phosphorus promotes healthy roots
what do fertiliser compounds contain
Fertiliser compounds contain the following water-soluble ions:
Ammonium ions, NH4+ and nitrate ions, NO3–, are sources of soluble nitrogen
Phosphate ions, PO43- are a source of soluble phosphorus
Most common potassium compounds dissolve in water to produce potassium ions, K+
what do fertiliser compounds contain
Fertiliser compounds contain the following water-soluble ions:
Ammonium ions, NH4+ and nitrate ions, NO3–, are sources of soluble nitrogen
Phosphate ions, PO43- are a source of soluble phosphorus
Most common potassium compounds dissolve in water to produce potassium ions, K+