Chapter 9 Flashcards
what is the law of conservation of energy
during physical and chemical processes energy may change form but it cannot be created or destroyed
if a chemical system gains energy the surroundings ______
lose energy
if a chemical system loses energy the surroundings _______
gain energy
what is exothermic
energy/heat exit the chemical system
what is endothermic
energy/heat enter the chemical system
what does exothermic result in
results in a decrease in chemical potential energy
what does endothermic result in
results in an increase in chemical potential energy
sign for exothermic
negative
sign for endothermic
positive
exothermic graph and where to label reactants and products
starts up (label reactants) and goes down (label products)
endothermic graph
starts down (label reactants) and goes up (label products)
what are the axis labelled in endo and exothermic graphs
x=reaction pathway
y=potential energy
Thermochemical equation for exothermic and description
A+B ——> C+D+ triangle H
energy is on PRODUCT side
Thermochemical equation for endothermic and description
A+B + triangle H —>C+D
energy is on REACTANT side
exothermic equation with triangle H notation
A+B—->C+D triangle H-_______
endothermic equation with triangle H notation
A+B—->C+D triangle H+_____
what is energy
the ability to do work
what is kinetic energy
energy of motion
what is potential energy
stored energy
what is heat
transfer of thermal energy
description of molecules in a temp change
gain or lose energy and move faster or slower
3 types of molecular motion
translational
rational
vibrational
what is chemical potential energy
energy stored in the bonds of a substance and relative intermolecular force
what is thermal energy
total kinetic energy of all of the particles of a system
what has more thermal energy a big or small object and why
a big object because it has more mass
what does temp do to thermal energy
increases it
thermal energy formula and units
Q=mctraingleT
Q= J
m= g
c=
T= degrees celsius
what is temperature
measure of the average kinetic energy of the particles in a system
lower heat capacity means (in terms of temp)
higher final temp
heat is not ______ by a system but is _________
heat is not possessed by a system but is energy flowing between systems
what is specific heat capacity
quantity of energy required to raise the temp of one gram of a substance by one degree
what is the density of water
1.00kg/L
mass formula in terms of density and volume
mass=density(volume)
what is calorimetry
technological process of measuring energy changes of an isolated system using a calorimeter
what does a calorimeter involve
a thermometer
stopper
2 styrofoam cups containing reactants in solution
calorimetry process (2 steps)
chemical is placed or dissolved in water
energy transfers between the chemical system and the surrounding way (is monitored by measuring changes in water temp)
exothermic example
hot pack
endothermic example
cold pack
calorimetry assumptions (list 5)
all energy is gained or lost by the calorimeter
all material is conserved
assume dilute solutions have the same properties of water
thermal energy gained or lost by the rest of the system is negligible
pressure remains constant in solutions and flame calorimetry
what is enthalpy
total kinetic and potential energy within a chemical system (energy possessed by system)
how is enthalpy communicated
the difference in enthalpy between react and and products
what is molar enthalpy
change in enthalpy expressed per mole of a substance undergoing a specific reaction
molar enthalpy formula and units
H= triangle H/n
H=(KJ per mol)
triangle H= Kj
molar enthalpy steps
1) write a balance question
2) determine knowns and unknowns
- make sure H is per mol
- divide by moles if not
3) find moles using unit analysis
4) solve for unknown using molar enthalpy formula
5) concert to desired units
molar enthalpy calorimetry steps
1) determine Q using thermal energy formula (combine both masses)
2) determine triangle H assuming triangle H= -Q
3) determine moles using unit analysis or concentration formula
4) determine molar enthalpy using molar enthalpy formula
flame calorimetry steps
same as molar enthalpy calorimetry
bomb calorimetry steps
1) write knowns and unknowns
2) determine unknown using Qcal=C(triangle t)
formula for bomb calorimetry
Qcal=C(triangle t)
thing to remember for final answer with molar enthalpy
may have to determine if endo or exothermic and indicate with plus or negative sign
molar enthalpy: finding n
1) steps 1 and 2 the same
2) skip to step 4
molar enthalpy: finding mass
1) steps 1 and 2 the same
2) skip to step 4 and 5
molar enthalpy calorimetry: finding mass
1) steps 1 and 2 the same
2) determine moles using molar enthalpy formula
3) concert to mass
molar enthalpy: finding Qcal/ Q any other total
1) determine Qcal using
Qcal= Qcan + Qwater
molar enthalpy: finding c
1) use mc(triangle t) 1 =-
mc(triangle t) 2
and manipulate for unknown c
flame calorimetry: finding t
1) determine moles of compound using unit analysis
2) determine triangle H using molar enthalpy formula
3) determine triangle t using - triangleH= Qcan + Qwater and manipulate for two t’s.
flame calorimetry: finding H using Qcal
1) determine Qcal using
Qcal= Qcan + Qwater
2) steps 2-5 the same
bomb calorimetry: heat combustion per gram
1) steps 1 and 2 the same
2) divide Q by mass
3) state value as KJ/g or J/g
