Chem unit 8 Flashcards
exothermic
chemical reaction that RELEASES heat
energy is on product side
delta H is negative
endothermic
chemical reaction that ABSORBS heat
energy on reactant side
delta H is pos.
does exothermic have a (-) or (+) q
(-)
does endothermic have a (-) or (+) q?
(+)
def of temperature
measure of the average kinestic energy of particles’ random motion
def of heat (q)
is a measure of the total amount of energy TRANSFERRED from a object or high temp –> object of low temp
unit for heat
joule/kilojoule/calorie
def of heat capacity
heat required to raise temp of an object by 1 degree celcius
def of specific heat
amount of energy needed to raise 1g of a substance 1 degree celsius
formula to calculate heat/energy flow
q=mc(delta)t
what is a system?
part of the world we want to study
ex. a reaction mixture in a flask
open system
exchange both matter and energy with surroundings
ex. open reaction can, rocket engine
closed system
can exchange only energy with the surroundings (matter remains fixed)
ex. sealed reaction flask
isolated system
can exchange neither energy nor matter with its surroundings
(ex. thermos flask)
is vaporization endo or exo thermic
endothermic- liquids must gain heat to boil and turn into gas!
is melting endo or exo thermic
endothermic- heat added to ice which is why it melts!
is freezing an endo or exo thermic
exothermic- heat is being lost which is why it turns to ice!
what is the first law of thermodynamics?
energy cannot be created nor destroyed, only converted from one form to another
True/False- substances with a high specific heat need more heat to change its temperature
true- high specific heat = stronger = small temp change when large amnt of heat added
enthalpy def
heat content of a system at a constant pressure
how to calculate enthalpy (deltaH)
delta H = Hprod-Hreac
free elements have what heat of formation?
ZEROOOO
requires energy to form a substance, will heat of formation be pos or negative?
positive or higher than 0 (endo)
releases energy when substance forms, heat of formation will be…
negative or lower than 0 (exo)
formula for heat of formation
deltaH_rxn = sum of delta H_fprod - sum of delta H_freact
phase diagram always goes in what order?
solid, liquid, gas (SLIG)
phase diagram- in a region, how many phases exist?
one!
phase diagram- how many phases exist?
two exist at equilibrium
phase diagram- how many phases exist at a triple point?
3 phases exist at equilibrium
note: pure substances only have one triple point
phase diagram- what is a critical point?
point where any higher temp/pressure, the substance can no longer exist as a liquid
(gas/liquid phases are indistinguishable)
standard temp and pressure
1 atm, 0 degrees celcius
sublimation
s –> g
vaporizatoin
l —> g
condensation
g —> l
Hess’ Law
possible to add two or more thermochemical equations to produce a final equation (another way to find enthalpy)
entropy
measure of the amount of disorder in a system
rank in order from least to most entropy!
solid, liquid, gas
how many directions can entropy go in?
two!
ex. solid to liquid or vice versa
what is a spontaeous reaction?
physical or chemical change that occurs with NO outside intervention at ordinary conditions
ex. ice being placed on a table and melting
does spontaneous mean quick?
NOOOO
ex. uranium takes years to decay but is still spont bc it occurs without outside intervention
if delta G is neg… spont or non-spont?
spont! (exothermic-releasing heat)
delta G pos –>
non-spontaneous
entropy equatoin
delta S = sum of products - sum of reactants
Gibbs free energy
combined enthalpy/entropy function that determines spontaneity of a process or the amount of energy that is left after a reaction takes place
gibbs equation
delta G = delta H - T x delta S
to find gibbs you must…
- determine enthalpy (deltaH)
- determine entropy (deltaS)
- subtract enthalpy from entropy
calorimetry
process of measuring the heat in chem. reactions
why do we use styrafoam cups in experiments?
good insulation
