energy and equilibrium Flashcards
(24 cards)
exothermic
chemical reactions in which heat is given out
bond making
endothermic
chemical reactions in which heat is taken in
bond breaking
calorimetry experiments
measures the amount of energy transferred in a chemical reaction.
measure temperature before and after the reaction.
use the mass of the liquid in the equation:
Q(amount of energy transferred) = mass x specific heat capacity x change in temp
specific heat capacity of water/ liquid
4.2 (4.18)
amount of energy transferred/ heat energy change
Q=MC x delta T
molar enthalpy change
delta H = Q x 10-3/ mols
BENDOMEX
breaking = endo
making = exo
bond energies to calculate enthalpy change
work out breaking (endo)
work out making (exo)
breaking - making = enthalpy change
practical: working out enthalpy change for combustion
measure 100cm3 of water
weigh a burner and record weight
use a thermometer, polystyrene cup
measure temp
stop after heating water about 20 degrees
calculate Q
calculate enthalpy moles, then enthalpy change
sources of error:
heat loss to surroundings (use plasticine cup)
conclusion: the larger the difference in the temperature the more energy is absorbed or released
reaction profile diagram
start off with reactants, second line is products
y-axis: energy
x-axis: time
exothermic: start off with higher line, include activation energy curve upwards, finish off with lower line.
endothermic: start off with lower line, activation energy, finish off with higher line.
reversible reactions
not all reactions are reversible
dehydration of anhydrous copper sulfate
endothermic
change from electric blue powder to white powder when heated (water is evaporated)
heat on ammonium chloride
on heating, white solid ammonium chloride decomposes forming ammonia and hydrogen chloride gas. On cooling, ammonia and hydrogen chloride react to form a white solid of ammonium chloride on the side of the tube
dynamic equilibrium
when the rate of the forward reaction is equal to the rate of the reverse reaction, so the products and reactants have constant concentrations.
conditions needed for a dynamic equilibrium
closed circuit and reversible reaction (sealed container)
catalysts effect on position of equilibrium
speeds up rate of reaction of both products and reactants, but no effect on position of equilibrium
increased temperature on position of equilibrium
shifts to the side of the endothermic reaction
justification: favours the reverse/forwards reaction because its endothermic
decreased temperature on position of equilibrium
shifts to the side of the exothermic reaction
justification: favours the reverse/forwards reaction because its exothermic
increased pressure on position of equilibrium
shifts towards the side with the least gas molecules
justification: favours the forward/backwards reaction because it has fewer gas molecules
decreased pressure on position of equilibrium
shifts towards the side with more gas molecules
justification: favours the forward/backwards reaction because it has fewer gas molecules
decrease concentration of reactant
shifts to the left/ side of reactants
justification: favours the reverse reaction because there are less reactants present
increase concentration of reactant
shifts to the right/ side of products
justification: favours the forward reaction because there are more reactants present
increase concentration of products
shifts to left/ side of reactants
justification: favours the reverse reaction because there are more products present
decrease concentration of products
shifts to the right/ side of the products
justification: favours the forward reaction because there are less products present
