water temperature and heat c/o physical science

Question

 

1.  at 3 degrees C, a volume of ice water is...

 

a.  contracting as it melts

b.  expanding as it melts

c.  less dense than ice

d.  done of these

 

 

2.  20 kg of lead are heated 2600 joules and its temperature rises 2 degrees C.  the same of water is heated 2600 joules and its temperature does not rise at all.  what might you conclude from this?

 

a.  water has a higher specific heat capacity than lead

b.  lead has a higher specific heat capacity than water

c.  water will cool faster than lead

d.  none of these

Answer 1

1.  Water has the peculiar property of becoming less dense as it freezes, but only for a small temperature range.  From 0 to 4 degrees Celsius, liquid water is denser than ice.  If this wasn't the case, ice wouldn't float!!  Most things become denser when they get colder (the molecular motion slows down, shrinking the volume of the substance).  So the answer is a.  When the ice melts, the liquid water is more dense than the ice, so it contracts.

 

2. Water has a specific heat capacity of about 10 times that of lead.  This means that water takes about 10 times as much heat energy to change its temperature by the same amount as lead.  This means that the 2600 J may change the temperature of the water by about 0.2 C, which would be almost unnoticeable with a lot of thermometers.  So the answer is a.