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What are the types of chemical reactions and what factors affect their…
What are the types of chemical reactions and what factors affect their rates?
What are the different types of chemical reactions?
Combustion
a substance reacts rapidly with an oxidant, usually oxygen, to produce heat and light
often in the form of a flame
Examples include burning wood in a fireplace, the combustion of fuel in a car engine, and the burning of gas in a stove.
Single-replacement
A + BC → AC + B
one element replaces another element in a compound
A common real-world example is the reaction between zinc and hydrochloric acid, where zinc displaces hydrogen from the acid.
Combination
A + B → AB
two or more substances combine to form a single, more complex product
An example includes burning of coal (carbon) in oxygen to produce carbon dioxide
Decomposition
AB → A + B
a single compound breaks down into two or more simpler substances
Double-replacement
AB + CD → AD + CB
two ionic compounds exchange ions to form two new compounds
Examples include water softening, baking soda and vinegar etc.
Neutralisation
Where an acid and a base react to form water and a salt. This reaction typically involves the combination of H+ ions (from the acid) and OH- ions (from the base) to produce water (H2O).
Redox
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Reactions involving the transfer of electrons between molecules or ions
Examples include rusting of iron, combustion, photosynthesis etc.
What are rates of a chemical reaction?
the speed at which reactants turn into products.
Measurements of rates
grams per second (g/s)
grams per minute (g/min)
cubic centimetres per second (cm3/s)
cubic centimetres per minute (cm3/min)
Formula:
What factors affect their rate?
Temperature
Raising the temperature provides reactant particles with more kinetic energy, leading to more frequent and energetic collisions. This increased energy increases the chances of particles overcoming the activation energy barrier. As a result, higher temperatures usually lead to faster reaction rates.
Concentration
Higher concentration of reactants means there are more particles in a given volume. This increase in particle density leads to more collisions per unit of time. As a result, reactions tend to happen more quickly as the concentration of reactants increases.
Surface Area
A larger surface area allows more reactant particles to be exposed and available for collisions. This is important in reactions involving solids. By breaking a solid into smaller pieces, you increase its surface area, speeding up the reaction.
Catalyst
substances that speed up reactions by providing an alternative reaction pathway with a lower activation energy
Not consumed during the reaction
Pressure
Increasing the pressure in reactions with gases compresses the gas particles into a smaller volume, leading to more frequent collisions. This increase in collision frequency can speed up the reaction rate. In closed systems, maintaining higher pressure results in faster reactions more often.
What is a chemical reaction?
Energy changes
Bond breaking and forming
Reactants
Starting materials
Products
New substances formed
Conservation of mass
Collision theory
Explains that for a chemical reaction to occur, reactant particles must collide with sufficient energy and the correct orientation. This energy must be equal to or greater than the activation energy, which is the minimum energy required to initiate the reaction. If particles collide with insufficient energy or incorrect orientation, no reaction will occur.
The rate of the reaction is directly proportional to the frequency of these collisions
Energy exchange
Exothermic reactions
Reactions that release energy, usually in the form of heat
Endothermic reactions
Energy is absorbed from the surroundings, usually in the form of heat. This results in a cooling effect as the system requires energy to break bonds in the reactants.
Electron transfers
Redox reactions
Reactions involving the transfer of electrons
Non-redox reactions
Reactions where there is no transfer of electrons
Bibliography:
Reference BYJU'S (2019). Rate of Reaction. [online] Byju’s. Available at:
https://byjus.com/chemistry/rate-of-reaction/.Purdue
University (2019). Calculating Rates. [online] Purdue.edu. Available at:
https://www.chem.purdue.edu/gchelp/howtosolveit/Kinetics/CalculatingRates.html
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