Topic 5 - Chemical Reactions Flashcards
What is an exothermic reaction ?
A reaction which overall gives out more energy to the surrounding areas (in the form of heat) shown by a rise in temperature
What is an endothermic reaction?
A reaction which overall takes in energy from the surroundings in the form of heat, shown by a fall in temperature.
Give an example of an exothermic reaction
Combustion Explosions
Give an example of an endothermic reaction
Photosynthesis Ammonium nitrate dissolving in water
Are endothermic or exothermic reactions more common?
Exothermic
What do you need to break bonds in a chemical reaction?
Energy
Which type of reaction is this?
Endothermic
What is the best way to measure temperature change in a reaction?
Take the temperature of each of the reactants and try to get them the same. Then put them in a polystyrene cup in a beaker with cotton wool in to insulate it then put a lid on the cup to prevent evaporation. Measure the temperature of the solution at the end.
Give an example of a slow reaction
The rusting of iron
Give an example of a moderate speed reaction
Metal reacting with acid
Give an example of a fast reaction
Explosion
What four things can affect the rate of reaction?
Temperature Concentration Catalyst Surface area
Why does temperature affect the rate of reaction?
The hotter the reaction the faster it is. The heat gives particles more energy so the move around more and it is more likely to get frequent successful collisions. It also provides them with enough energy to break the bonds.
Why does concentration affect the rate of reaction?
The higher the concentration the faster the reaction. There are more particles so there will be a higher frequency of successful reactions.
how does a catalyst affect the rate of reaction
A catalyst will speed up the rate of reaction by lowering the amount of energy required by the reactants to react. They increase the frequency of successful collisions.
How does surface area affect the rate of reaction?
The bigger the surface area the faster the reaction. There are more particles near the surface so more frequent successful reactions will take place.
Describe an experiment to test the effects of concentration or surface area on rate of reaction.
Put HCL and marble chips in a conical flask and but a gas syringe on it. Time how long it takes to get to a certain volume of gas. For concentration - repeat with different concentrations of HCL. For surface area - repeat with same mass but different sized marble chips.
Describe an experiment that can be used to show the effect of temperature on rate of reaction
But a flask on a piece of paper with a cross on it. Mix Sodium Thiosulfate and HCL together and time how long it takes the cross to be no longer visible. Change temperature of sodium Thiosulfate to see the affects.
Give an example of where a catalyst converter can be found
Vehicle exhaust. They are used to increase the rate that carbon monoxide and unused fuel react with oxygen to produce carbon dioxide and water. The catalyst has a large surface area and works best at high temperatures.
What is collision theory?
more collisions increases the rate of reactions
Name two common processes that use catalysts
the Haber process to make ammonia (iron)
hydrogenation of margarine (nickel)
