C2 - Rates & Energy
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How is rate of reaction calculated?
amount of reactant used or product formed / time
What is the rate of a chemical reaction?
How fast reactants turn into products.
What are the four main factors that affect rate of chemical reaction?
• Temperature • Surface area • Concentration or pressure • Presence of a catalyst
What is collision theory?
Particles have to come together with enough energy to react.
What is activation energy?
The smallest amount of energy particles must have before they can react.
How does surface area affect rate of reaction?
A larger surface area increases the frequency of collisions between reactants.
How does temperature affect the rate of reaction?
The rate of reaction increases with temperature.
Why does temperature affect the rate of reaction?
• Particles collide more often. - Particles collide with more energy.
How does concentration affect the rate of reaction?
The greater the concentration, the greater the rate of reaction.
Why does increasing the concentration affect the rate of reaction?
More particles in the same volume increases the frequency of collisions.
What is a catalyst?
A chemical which speeds up the rate of reaction.
Why are catalysts used in industry?
The cost of precious metal is often less than the extra cost of energy.
Why are catalysts better for the environment?
Fossil fuels are used to produce the energy for reactions without catalysts.
How can catalysts be harmful for the environment?
Transition metals used as catalysts are often toxic and can escape into the environment.
What is an exothermic reaction?
A reaction that transfers energy to the surroundings.
What is an endothermic reaction?
A reaction which transfers energy from the surroundings.
What type of reaction is oxidation?
Exothermic
Give three examples of exothermic reactions.
• Burning • Respiration • Neutralisation
Give an example of an endothermic reaction.
Thermal decomposition
How do disposable hand warmers work?
Iron is oxidised to become hydrated iron(iii). Sodium chloride is used as a catalyst.
How do reusable hand warmers work?
Clicking a metal button starts the crystallisation of a supersaturated solution of sodium ethanoate. The crystals spread and give out energy. The warmer can be reused by redissolving the crystals using boiling water.
What is the general equation for self heating cans?
calcium oxide + water —-> calcium hydroxide
How do instant cold packs work?
When ammonium nitrate dissolves in water it takes in energy.