energy changes Flashcards
energy
is conserved in chemical reactions
energy is same before and after reactions
exothermic
energy transferred to the surroundings
temp of surroundings increase
examples
combustion
oxidation
neutralisation
used self heating cans
hand warmers
exo exits
endothermic
energy taken in from surroundings
temp of surrounds decrease
examples
thermal decomposition
citric acid and sodium hydrogencarbonate
used in ice packs
endo enters
apparatus
polystyrene cup thermometer 250cm^3 glass beaker measuring cylinder top pan balance
endothermic reactions
acid w/ alkalis
acids w/ metal carbonates
exothermic reactions
neutralisation
displacement
acids w/ metals
method
polystyrene cup in glass beaker
measure 20cm^3 of solution and add to cup
record temp
measure appropriate mass of solid/liquid
add to cup with solution
record high/lowest temp
analysis
bigger temp change more energy released /absorbed
evaluatio/ error
to prevent unwanted heat transfer insulate cup with polystyrene and use lid
hazards
acids/ alkalis
metal salt solution ( in displacement)
risks
irritate skin/ eyes
dangerous to environment
precaution
avoid direct contact with skin / wash hands / eye goggles
dispose metal salt solution safely / collect rather then pour down drain
reaction profiles
shows whether reaction is endo/exo
show reactants/ products
reaction profile = exo
energy level decrease - energy given to surroundings
-ve negative reactants have more energy feels hot bonds are made energy = chemicals - surroundings
enthalpy change = negative
reaction profile = endo
energy level increase - energy taken in from surroundings
\+ve positive products have more energy feels cold energy surroundings to chemicals bonds broken
enthalpy change = positive
