2b) Reaction Rates, Salts and Electrolysis Flashcards
What are the four factors affecting the rate of a reaction?
Temperature
Concentration
Catalyst
Surface area of solids
(Or pressure for gases)
(Or size of solids)
How do you work out the rate of a reaction?
Amount of reactant used or product formed / time
How do you know what reaction is the quickest on a graph?
Line with the steepest slope
Why do lines representing quicker reactions become flat earlier on graphs?
Faster reaction = sooner it finishes
What are the three different ways the rate of reaction can be measured?
Precipitation - time for solution to turn cloudy (cross disappears)
Change in mass - quicker the mass drops, faster the reaction
Volume of gas given off - more gas in given time, faster the reaction
What are the pros and cons of each method to measure the rate of a reaction?
Precipitation - very subjective to view of when the mark disappears
Change in mass - most accurate, only if gas produced, however can be inaccurate if mass lost by evaporation if flask is hot
Volume of gas given off - only works if gas produced, plunger from syringe could come out easily
How does using finer particles (powders instead of solids) affect the rate of reaction?
Larger surface area
More frequent collisions
Rate of reaction is faster
(collision theory)
Name four rate of reaction experiments
HCl and marble chips - affect of surface area
Magnesium metal with dilute HCl - affect of concentration
Sodium Thiosulphate and HCl - affect of temperature
Decomposition of Hydrogen peroxide - affect of catalysts
What is the collision theory?
Rate of a reaction depends on how often and how hard the reacting particles collide successfully with each other
Why does higher temperature increase the rate of a reaction?
Temperature increased
Particles move quicker due to more energy provided by heat
More collisions, more often
Faster reaction (collision theory)
Why does higher concentration increase the rate of a reaction?
More concentrated solution
More particles of reactant
More collisions, more often
Faster reaction (collision theory)
Why does higher pressure increase the rate of a reaction?
More pressurised gas
More squashed up particles
More collisions, more often
Faster reaction (collision theory)
Why does larger surface area increase the rate of a reaction?
Later surface area/ smaller solid pieces
More particles exposed to more reactant pieces
More collisions, more often
Faster reaction (collision theory)
What is activation energy?
The minimum amount of energy needed by particles to react
What is a catalyst?
Substance which speeds up a reaction without being changed or used up itself in the reaction
What are the advantages of catalysts in industrial reactions?
Reduces costs by:
Speed up reaction - plant doesn’t need to operate as long - cheaper
Lower temperatures - lower energy costs - also better sustainability
Can be used over again as they aren’t used up in the reaction - no need to buy replacements
What are the disadvantages of catalysts in industrial reactions?
Expensive to buy
Often need to be removed and cleaned
Only catalyse a particular reaction - may need to buy more than one
Can be denatured or poisoned
What happens to energy during chemical reactions?
Transferred to or from the surroundings
What is an endothermic reaction?
A reaction which takes in energy (heat) from the surroundings and creates a fall in temperature
