enthalply Flashcards
what does exothermic mean
energy is released to the surroundings
what does endothermic mean
energy is taken in from the surroundings
why type of process is bond breaking and why
endothermic, system gains energy from surroundings
what happens to the surroundings in an endothermic reaction
they get colder because the reaction takes in energy
what type of process is bond making and why
exothermic, energy is given to the surroundings
what happens to the surroundings in an exothermic reaction
get hotter
what is energy changed called, and what is its units
enthalpy KJ/MOL
when is enthalpy positive
when heat energy is taken in - endothermic
when is enthalpy negative
when heat energy is given out - exothermic
energy profile for an exothermic reaction
It has a negative enthalpy change, you are giving out energy so the products will always be lower than the reactants
energy profile for endothermic reaction
positive enthalpy change as it takes energy in. As it takes energy in the products will always be higher than the reactants.
enthalpy change definition
overall energy change of a chemical reaction
bond energy definition
energy needed to break a particular covalent bond
catalyst definition
speeds up rate of reaction and is chemically unchanged, provides an alternate reaction with a lower activation energy.
activation energy definition
minimum energy needed for a reaction to start
energy profile with catalyst
how do you calculate enthalpy from bonds
do bonds broken and bonds made and do broken - made
heat energy transferred equation
heat energy transferred (Q) = mass of liquid heated (g) * specific heat capacity * temp change
how do you convert heat energy (Q) to enthalpy (H)
enthalpy = - heat energy / moles
how do you work out moles of an acid
concentration * volume (cm3/1000)
what is the main source of error in enthalpy practicals and how is this avoided
heat loss - use insulation e.g polystyrene cup and surround with more insulation
what is the problem with enthalpy combustion reactions
incomplete combustion results in a build up of soot ( insulator) , alcohols are volatile (evaporate easily) so mass can be lost as soon as the lid is removed.
what type of reaction is neutralization
exothermic
what do you react in neutralisation
HCL and sodium hydroxide
