Topic 5- Energy changes Flashcards
definition of conservation of energy
energy cant be created or destroyed
whats an exothermic reaction
one which transfers energy to the surroundings, usually by heating. This is shown by a rise in temperature
whats an example of an exothermic reaction
burning fuels (combustion)
neutralization
oxidation reactions
everyday uses of exothermic reactions
hand warmers(iron in air) self heating cans of hot chocolate/coffee
whats an endothermic reaction
one which takes in energy from the surroundings, shown by a fall in temperature
examples of endothermic reactions
citric acid and sodium hydrogencarbonate
thermal decomposition
everyday uses of endothermic reactions
used in sports injury packs
explain the exothermic reaction profile
the products are at a higher height than the reactants.
what does the difference in height represent
the difference in height represents the overall energy change in the reaction,
whats activation energy
the initial rise in energy represents the energy needed to start the reaction
OR YOU COULD SAY
the minimun amount of energy the reactants need to collide with each other and react.
the greater the activation energy….
the more energy needed to start the reaction. this has to be supplied eg. by heating the reaction mixture.
describe an endothermic reaction profile
the products are at a higher energy than the reactants
what happens, in terms of bonds, in a chemical reaction?
old bonds are broken and new bonds are formed
describe endothermic reactions in terms of bonds
ENDOTHERMIC = BREAKING BONDS
energy must be supplied to break existing bonds
describe exothermic reactions in terms of bonds
EXOTHERMIC= FORMING BONDS
energy is releases when new bonds are formed
explain the energy amounts in endo and exo thermic reactions
exo- energy released by forming bonds > energy used breaking bonds
endo- energy used to break bonds > energy released forming bonds
equation for overall energy change
energy required to break bonds - energy released by forming bonds
whats an electrochemical cell
system made up of TWO different ELECTRODES in contact with an electrolyte
whats an electrolyte
a liquid that contains ions which react with the electrodes
what causes voltage
different metals reacting differently with the same electrolyte
the bigger the difference in reactivity of the electrodes…
the bigger the voltage of the cell
how does the electrolyte used in a cell affect the size of the voltage
different ions in solutions will react differently with the metal electrodes used
how is a series battery formed
connecting 2 or more cells together, the voltages of the cells in the battery are combined so there is a bigger voltage overall
