energy changes Flashcards
endo vs exo
exo: energy TO the surroundings
endo: energy FROM the surroundings
do endo or exo reactions increase temperature
increase: exo
decrease: endo
what does an exothermic reaction look like on a graph
products is lower
what does an endothermic reaction look like on a graph
products are higher
what is activation energy and what does it look like on a reaction profile
minimum amount of energy needed for a reaction to happen
space between reactant and peak graph
reaction profileof exo vs endo
exo: products is lower
endo: products are higher
what shows energy taken in/given out on a reaction profile
difference between energy of reactants and energy of compounds
4 examples of exothermic reactions
oxidation
combustion
neutralisation
hand warmers
2 examples of endothermic reactions
thermal decomposition
sports injury ice packs
what is activation energy
minimum energy that particles must have for a reaction to occur
what shows activation energy on reaction diagram
difference between reactants and peak of curve
what shows energy change in a reaction and why
bond breaking - bond making
bond breaking requires energy (exo) so is positive, as energy is gained, while bond making transfers energy (exo) so is negative, as energy lost
how to calculate the energy change in a reaction
- reactant bonds are being broken, product bonds are being made
- write bond energy values of reactants and products and multiply by number of molecules (large number)
- add reactants together & products together
- bond breaking - bond making
- if answer is negative, reaction in exo, energy has been transferred to surroundings
investigate how conc of sodium hydroxide affects temp change in the neutralisation reaction between HCl and sodium hydroxide
- measure 30cm^3 of dilute HCl using cylinder, pour into polystyrene cup
- stand cup in a beaker to avoid toppling
- record temp of acid using thermometer
- measure 5cm^3 sodium hydroxide solution using cylinder, transfer to polystyrene cup
- add a plastic lid with thermometer through a hole and gently stir
- reaction is exo, so record highest temp reached when the reading stops increasing
- rinse and dry polystyrene cup
- repeat, adding 5cm^3 sodium hydroxide solution each time until maximum 40cm^3 is reached
- repeat whole experiment again and calculate mean of max temp
- plot max temp x volume added graph
why does the polystyrene cup need a lid when investigating temp change of a reaction
to reduce heat loss
polystyrene is good thermal insulator, reduces heat loss from sides and bottom, and lid reduces heat loss to air
how does a graph look for investigating how conc affects temp change in
increases to a point, then stops, and begins to decrease
why does concentration of sodium hydroxide increase temp change in the reaction at first
volume increases, there are more particles to react with HCl, and these reactions are exo, releasing energy and increasing max temp reached
why does concentration of sodium hydroxide stop increasing temp change in the reaction at a certain volume
some NaOH particles are unable to react as there are too many with not enough HCl. in other words, amount of energy released by reaction has reached a maximum
why does concentration of sodium hydroxide start to decrease temp change in the reaction
there is a greater volume of solution for each experiment, meaning energy release is spread out over a greater volume
how do rechargeable batteries work
chemical reactions reverse when electrical current applied
how does a cell work
- two metals, connected to voltmeter by wire, placed in an electrolyte
- a pD will generate between electrodes and electic current will flow through wires
- energy produced from reactions on the electrodes
limitations of cells
- electricity only produced for certain amount of time, as chemicals eventually run out and reaction stops
- no electricity produced if metals have same reactivity
how can electricity produced in a cell vary
metals used
larger difference in reactivity = larger PD
- more charge able to flow
electrolyte used
what is a battery
two or more cells connected in series to produce a greater voltage
