Answer 1:
The speed at which water heats up has to do
with its heat capacity. Heat capacity is the
amount of heat energy it requires to heat a gram
of material one Kelvin degree. The higher the
heat capacity, the more slowly the water will
heat, given the same amount of energy added. The
heat capacity of freshwater is 4.182 J/(g K) and
the heat capacity of saltwater is 3.993 J/(g K).
Therefore, saltwater will heat up faster than
freshwater.
One thing to keep in mind is that heat
capacity is based on the mass of a material and
not its volume. That is to say, given the same
amount of heat added, the same mass of saltwater
will heat faster than freshwater. If you want to
compare the same volume, then you need to know
the densities. The density of freshwater is
998.21 kg/m^3 and the density of saltwater is
1024.75 kg/m^3. From the heat capacities and
densities, we can calculate that given the same
mass, saltwater will heat 5% faster than
freshwater, but given the same volume it will
only heat 2% faster because it is denser. These
numbers will be different for different salt
concentrations and also for temperature, because
heat capacities and densities depend on salt
concentration and temperature. All of the
numbers I used above are given at 20°C with a
salt concentration of 35 g/kg of salt in water.
Also, here is an excellent explanation:
expl
anation, please click here
References:
http://www.kayelaby.npl.co.uk/general_physics/2_7
/2_7_9.html
http://www.swri.org/10light/water.htm
http://en.wikipedia.org/wiki/Properties_of_water
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