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
activation energy
minimum energy needed for particles when they collide
shown as hump
breaking bonds
endo
taken in
more energy needed for breaking bonds in reactants
making bonds
exo
given out
more energy needed when making bonds in products
reactivity series
larger gap
larger pd
sample cell
2 electrodes
voltmeter
electrocyte solution
cell safety
salt solution in eyes
wear safety goggles
increase voltage
combine 1 or more cells
over time voltage decreases as electrode is used up
hydrogen fuel cells pros
no carbon emissions
releases lots of energy
uses energy efficiently
hydrogen fuel cells cons
hydrogen is highly reactive
hydrogen requires a lot of space
hydrogen is hard to transport
endo thermic
energy is taken in from surroundings
products have more energy than reactants
+positive enthalpy change
energy is used to break bonds
