Molecular Steam
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physics!! help!?
1) Explain in molecular terms, why considerable heat energy is needed to convert 1g of water into 1g of steam at 100°C, without any temperature change taking place.
2) In an experiment, 120g of ice at 0°C is to be melted. the specific latent heat is of ice is 340J/g. Assume all the energy from the heater is going to be used to melt the ice.
Calculate the expected time for which the 60W heater is switched on.
(please explain answers!!)
first question:
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in order to boil water, you must compeletely separate the water molecules from each other. however, water molecules exert attractive forces on each other. these attractive forces are called hydrogen bonds. since hydrogen bonds are relatively strong, it's hard to break them, which means a large amount of energy (in the form of heat) is required to separate the water molecules from each other.
the reason why the temperature doesn't change during the liquid to vapor phase change is becasue the energy that is being added is being used to break those hydrogen bonds between the water molecules. therefore the energy is *not* being used to increase the kinetic energy of the molecules (which would cause the temperature to increase)
second question:
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first determine the amound of energy needed to melt the water:
120 g x [340 J / 1 g] = 40800 J
since the heater is 60 W, it's supplying heat at a rate of 60 J per second:
60 J = 1 s
we can now determine how much time is required for the heater to melt the ice:
40800 J x [1 s / 60 J] = 680 s
Autoclave use in Molecular Biology Lab
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