Topic 5 - Physical Chemistry Flashcards
exothermic reaction
gives off heat to surroundings
reactants have more energy than products
endothermic reaction
takes in heat from surroundings
products have more energy than reactants
activation energy
minimum amount of energy the particles need to collide and react
activation energy on graph
from reactants to peak of curve
breaking bonds
requires energy
endothermic reaction
making bonds
does not require energy
exothermic reaction
bond energy
amount of energy required to breaj one mole of a particular covalent bond
calculating overall energy change
energy required to break bonds - energy released by forming bonds
or
energy of reactants - energy of products
energy change of exothermic reactions
negative
as heat is being released
energy change of endothermic reactions
positive
as energy is taken in
measuring rate of reaction
quantity of products formed / time taken
or
quantity of reactants used / time taken
how does temperature affect rate of reaction?
increased temp = particles have more kinetic energy
= particles collide more frequently
therefore, more successful collisions occur
resulting in a higher rate of reaction
how does concentration affect rate of reaction?
increased concentration = more particles
= particles collide more frequently
therefore, more successful collisions occur
resulting in a higher rate of reaction
how does surface area affect rate of reaction?
increased surface area = particles can collide more frequently
therefore, more successful collisions occur
resulting in a higher rate of reaction
how does a catalyst affect rate of reaction?
catalyst provides alternate pathway with lower activation energy, so rate of reaction is higher
catalyst
substance that increases the rate of reaction without being chemically changed or used up.
reversible reactions
a chemical reaction in which the reactants react to form the products and the products can react to form the original reactants
reversible reaction symbol
⇌
reversible reaction - dehydration of hydrated copper (II) sulfate
hydrated copper (II) sulfate: blue hydrated crystals
- turn into white anhydrous powder upon heating
- reverse occurs when water is added back
- endothermic forwards reaction, exothermic reverse reaction
reversible reaction - application of heat to ammonium chloride
ammonium chloride: white solid
- decomposes into ammonia (NH₃) and hydrogen chloride (HCl) gases when heated
- these gases can combine again to form ammonium chloride when cooled
dynamic equilibrium
the rate of the forward reaction equals the rate of the reverse reaction and the concentrations of the reactants and products remain constant.
- this can be reached in a closed system ONLY
why does a catalyst not affect the position of equilibrium in a reversible reaction
A catalyst increases the rate of a reaction by speeding up the forward AND reverse reactions EQUALLY
This, therefore, helps a reversible reaction reach equilibrium quicker and does not affect the position of equilibrium.
increase in temperature
shifts the position of equilibrium in the direction of the endothermic reaction
decrease in temperature
shifts the position of equilibrium in the direction of the exothermic reaction
