Which costs more energy: changing 5 kg of ice into water at 0 C, ...

[awywial]

Which costs more energy: changing 5 kg of ice into water at 0 C, or changing 5 kg of water at 100 C into steam at 100 C?
 
  What will be an ideal response?

Question 2

Nuclear energy could be part of the answer to the danger of the world's greenhouse warming.
 
  What will be an ideal response?

[memslove]

Answer to Question 1

To change 5 kg of ice to water at 0 C, we need 5 kg x 333 kJ/kg = 1665 kJ. To
change 5 kg of water to steam at 100 C, we need 5 kg x 2.25 MJ/kg = 11.25 MJ. Clearly,
the energy needed to change water to steam is greater than that needed to change ice to
water.

Answer to Question 2

This is the case in the short term (say, for the coming century). Thermal systems
contribute waste heat, and if all the world's energy comes from thermal systems, there will
be a net increase in thermal energy directly from warming Earth.

[awywial]

Thanks for the timely response, appreciate it

[bitingbit]

Excellent