temperature and heat Flashcards
what is the difference between heat and temperature?
heat is the added kinetic energy of molecules within a substance. i.e. how much thermal energy the substance holds.
temperature is the measurement of heat emitted by an object i.e. ability of an object to transfer heat energy.
thermal energy travels from object of higher temp to colder temp
what is normal core body temp?
36.5 to 37.5
what is absolute 0?
Kelvin = 0
equivalent to -273.15 degrees C
no colder temperature exists.
what is the target ambient temp and humidity in theatre?
22 to 24 degrees C
50-60 % humidity
describe the differences between solid, liquid and gas.
solid:
- organised molecules
- strong intermolecular bonds
- fixed shape
- lowest amount of kinetic energy of the states
liquid:
- weak intermolecular bonds
- can break and reform such that can change shape to occupy container
- more kinetic energy than solids.
gas:
- no bonds between molecules
- molecules move freely and randomly
- expand to fill container
- space between molecules is larger than molecules
- highest kinetic energy
BONDS, SHAPE, ENERGY
what is meant by latent heat of fusion and vaporisation? and specific heat of these?
latent heat of fusion = energy required to break bonds of solid to it change state to a liquid without changing its temperature (temp of surroundings will change)
specific latent heat of fusion = the heat required to convert 1kg of solid at its melting point into a liquid at same temperature. (J/ kg)
same for latent heat of vaporisation except from liquid to gas
draw a graph to demonstrate the latent heat of fusion and vaporisation..
As heat is supplied to a solid, its kinetic energy will increase and temperature will increase.
When its melting point is reached, the heat energy will be used to break the bonds and thus there will be no change in temperature as it is converted to a liquid.
the same happens again when liquid is vapourised to gas
x axis = heat suplied
y axis = temperature of the substance
gradient goes up linearly but with plateaus for latent heat of fusion (solid to liquid) and then again for latent heat of vaporisation (to a gas)
give example of when latent heat of vapourisation is seen in threatre and how this is minimised?
Vaporisers - as sevo vapourisers, heat is taken from surrounding for latent heat. needs temp compensation mechanism
N20 canister - as N20 evapourates with use out of canister, the canister cools because heat has been taken from surroundings.
heat loss from laparotomy / skin preps - open abdomen leads to evaporative losses - uses patients body heat hence can lead to hypothermia. Can put exposed bowel in plastic coverings.
HME filters - reduce evaporative losses from humidying air. air is already supplied with humidified water so no energy is needed to evaporate water.
what is meant by specific heat capacity?
heat capacity = the energy required to raise the temp of a substance by 1 degree C
specific heat capacity = the energy required to raise the temp of 1kg of a substance by 1 degree C = Joules/Kg/Kelvin
(doesnt matter if in K or degrees as the difference of 1 degree C is same as 1 K i.e. just shifted by 273.15)
what is the specific heat capacity of water?
4.18 joule/kg/kelvin
how is specific heat capacity calculated?
c = joules of energy needed / (temp change x mass)
C = J / (ΔT × m)
what is molar heat capacity?
the amount of energy required to increase temp of 1 mole of a substance by 1 degree
what is the zeroth law of thermodynamics?
If 2 systems are in thermal equilibrium with a 3rd they are also in equilbrium with eachother.
hence energy will be transferred until all 3 are in equilibrium i.e. the middle object acts as a conduit and the other 2 objects dont need to be directly touching.
what is the first law of thermodynamics ?
energy is not created or destroyed
only converted from one form to another
what is the second law of thermodynamics?
entropy of the universe is always increasing with time
