Rates and energy Flashcards
Three ways of measuring rates of reactions
Measure decreasing mass of reactants over time
Measuring increasing amount of products over time
(With precipitate reactions) measuring the decreasing light passing through a solution
Equation for rate of reaction
rate of reaction = amount of reactant used or amount of product formed ÷ time
Four factors that affect rate and why?
Temperature - particles collide more often and with more energy so a higher proportion of particles have activation energy
Surface area - more particles exposed to be surrounded by the other reactant
Concentration/pressure - same as temperature
Presence of a catalyst
Define activation energy
The smallest amount of energy particles need before they can react
Three main points about how catalysts work
They speed up rates of reactions
They are not used up in reaction
Different ones are needed for different reactions
Why are catalysts used?
To increase rate of reaction (decrease time taken) and to reduce energy costs
What type of substance are catalysts often made from and why might this be a downside?
Transition metals and their compounds, which can be toxic and harm the environment if they escape
They can be rare and so expensive
Define exothermic and endothermic
EXOthermic - transfers (heat) energy from the reactants to their surroundings
ENDOthermic - transfers (heat) energy from the surroundings to the reacting chemicals
Give two examples of exothermic reactions and two everyday uses
Combustion, neutralisation
Self-heating cans, hand warmers
Give one example of an endothermic reaction and one everyday uses
Thermal decomposition
Sports injury packs
Describe the energy transfers in a generic reversible reaction
The amount of energy released when the reaction goes in one direction is equal to the energy absorbed when it goes in the opposite direction
If hydrated copper sulphate produces anhydrous copper sulphate and water(g) with heat and is an endothermic reaction, what happens when water is added to anhydrous copper sulphate?
It produces hydrated copper sulphate and is exothermic (releases heat)
