the minimum amount of energy needed by colliding particles in order for a reaction to happen
describe an exothermic change/reaction ?
a change or reaction in which heat energy is given out
describe an endothermic change/reaction ?
a change or reaction in which heat energy is takenin
what do exothermic changes do to a solutions temperature ?
increase if in solution
what do endothermic changes do to a solutions temperature ?
decrease if in solution
how do reactions occur ?
reactions occur when particles collide
what increases the rate of reaction ?
increased frequency
energy of collisions
increased temperature
reactant particles move more quickly
exothermic reaction profile
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endothermic reaction profile
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explain an exothermic reaction profile ?
energy level of the reactants is greater than the energy level of the products
the energy change is negative (transferred to surroundings)
explain an exothermic reaction profile ?
energy level of the reactants is lower than the energy level of the products
the energy change is positive (transferred from surroundings)
how does surface area to volume ratio effect the rate of reaction ?
the rate of reaction increases when the surface area : volume ratio of a solid reactant increases (lumps made into powder)
more particles of reactant are available
the frequency of successful collisions increases
how does a large piece of material effect the rate of reaction ?
smaller surface area
slower reaction
how does a large piece of material effect the rate of reaction ?
larger surface area
faster reaction
a catalyst provides an alternative reaction pathway that has a lower activation energy than the uncatalysed reaction
how does the addition of a catalyst increase the rate of reaction ?
adding a catalyst increases the frequency of successful collisions because a greater proportion of collisions now exceeds this lower activation energy
the overall heat energy change for a reaction is exothermic if ...
more heat energy is released in forming bonds in the products than is required in breaking bonds in the reactants
the overall heat energy change for a reaction is exothermic if ...
less heat energy is released in forming bonds in the products than is required in breaking bonds in the reactants
whats a catalyst ?
a substance that speeds up the rate of reaction without altering the products of the reaction being itself unchangedchemically and in mass at the end of the reaction
how does changes in temperature effect the rate of reaction ?
the rate of reaction increases when the temperature increases as the particles gain energy
reactions increase when temp increases as...
the particles move faster
the frequency of collisions increases
the energy of collisions increases so a greater proportion of collisions are successful
how does concentration and pressure effect the rate of reaction ?
the rate of reaction increases if the concentration of a dissolved reactant increases, or if the pressure of a reacting gas increases
reactions increase with an increased concentration as..
there are more particles in the same volume
the frequency of successful collisions increases
whats the heat energy change for a salt dissolving in water ?
can be exo or endo depending o the salt used
( temp can change due to precipitate of salt)
whats the heat energy change of neutralisation reactions ?
can be exo or endo but its usually exothermic
whats the heat energy change of displacement reactions ?
exothermic
whats the heat energy change of precipitation reactions ?
can be exo or endo depending on the substances involved
when these reactions take place in solution, temperature changes can be measured to reflect the heat changes
what units are the energies of bonds given in ?
( KJmol-1)
how to calculate the energy change in a reaction given the energies of bonds ?
add together the bond energies for all the bonds broken in the reactants ("energy in")
add together the bond energies for all the bonds formed in the products ("energy out")
energy change = in-out
the steeper the line the greater the rate of reactions
fast reactions finish sooner
whats an acid ?
a compound that dissolves in water to form a solution with a PH of less than 7
whats an alkali ?
a compound which dissolves in water to form a solution with a PH of more than 7
whats bond energy ?
the energy needed to break one mole of a covalent bond is its bond energy, measured in kilojoules per mole
whats collision theory ?
the reactant particles can only react with eachother when they bump into one another