topic 3 heat

Created by

phoebe

Cards (27)

$q=$ $mcΔt$  
where
q = energy
m = mass
c = specific heat capacity
Δt = change in time
$q=$ $mL$  
where
q = energy
m = mass
L = latent heat capacity
phases changes use potential energy, the energy between molecular bonds, while heat changes are kinetic energy, given by heat or speed changes of the molecules
in a solid, molecules can only vibrate, not translate
in a liquid, molecules can vibrate and move freely in a fixed volume
in going from a solid to liquid, some intermolecular bonds are broken and allow the molecules freedom for motion
in going from a liquid to a gas, most of the intermolecular bonds are broken
sublimation is going from a solid to a gas. deposition is going from a gas to solid
$E_{int}=$ $E_k+$ $E_p$  
where
internal energy = kinetic energy + potential energy
the thermometer measures kinetic energy; thus when a substance is going through a phase change, the temperature will not change. The energy that is being transformed when adding heat is the potential energy between the intermolecular bonds being broken.
the celcius degree at which every gas attains a pressure of 0 is at -273 degrees celcius
kelvin: the SI base unit of thermodynamic temperature (equivalent in size to the degree Celsius). its 0 starts at celcius's -273
one kilocalorie is the amount of heat needed to raise one kilogram of water by 1 degree celcius
1 kcal = 4.186kJ
for food, calories are really a kilocalorie (kcal)
$473 Cal=$ $473Cal*$ $(4.186kJ)/(1Cal) =$ $1143kJ$  
example: if a snickers bar is 473 calories, how many joules is it?
$p=$ $m/v$  
pressure = mass/volume
example: air has a density of about p=1.2kgm^-3.
How much het, in joules, is needed to raise the temperature of the air in a 3m by 4m by 5m room by 5 degrees celcius?
*air's specific heat capacity is =1050
solution:
formula: mcΔT
c=1050
ΔT=5

step 1:
find m
p=m/v
(1.2)=m/(3*4*5)
1.2*60=m
m= 72

thus,
(72)*(1050)*5= heat needed
heat needed is 37000J
(ideal gas) p=F/A 
where
p= pressure
F= force
A= area

p here describes the pressure that the walls of the box feel exerted by the molecule within it (newton's third law, molecule exerts an equal and opposite force on the walls of the box)

units:Nm^-2, Pascals (Pa)
$n=$ $N/N_a$  
where
n= number of moles
N= number of atoms
N_a= Avogadro's constant
ideal gas law
$pV=$ $nRT$  
where
p=pressure
v=volume
n= number of moles
R= gas constant
T= temperature
average kinetic energy per molecule of gas
$E_k=$ $(3/2)k_bT$
or $E_k=$ $(3/2)(R/N)T$  
where
K_b= boltzmann's constant
R= gas constant
N= number of atoms
an ideal gas is an imaginary gas that is used to model real gases
are identical perfect spheres
are perfectly elastic, dont lose any kinetic energy during collisions with each other or the walls of their container
have no intermolecular forces - potential energy does not change when heated
are so small that their volume is much smaller than the volume of their container
kinetic model of an ideal gas:
if temperature of gas increases, so does average speed (and hence kinetic energy) of the molecules
higher speed and temperature means more collisions with container walls. thus: higher pressure
avagadro's number
6.02*10^23
*1 mol = 6.02*10^3 of something
atomic weight is the highlighted number in a square in the periodic table
find
the gram atomic weight of water
the mass in grams of 1 mole of water
how many moles of hydrogen and oxygen there are in 1 mole of water 
GAW of water (H_2O) is given by 2*(1.00794)+1(15.9994) = 18.01528g per mole.
thus that is the mass of 1 mole of water
since each mole of H2O has 2H and 1O, there are 2 moles of H and 1 mole of O for each mole of water