Question

Which describes the temperature changes that would be observed as ice at −15 degrees Celsius is changed to water at zero degrees Celsius?

steady increase in temperature from −15°C to 0°C with gradual change from ice to water

gradual increase in temperature of ice from −15°C to 0°C, holding at 0°C as ice melts to water

steady decrease in temperature from water at 0°C to ice at −15°C

holding at −15°C as ice melts to liquid water and then gradual warming of water to 0°C

Answer 1

Answer: gradual increase in temperature of ice from −15°C to 0°C, holding at 0°C as ice melts to water

Explanation: The heat used to convert solid to liquid is gained by molecules to gain kinetic energy and thus the molecules start moving faster and the temperature increases.

But as the melting point is approached i.e.
`0^oC`, the temperature remains constant as now the heat given is used to break the inter molecular forces and thus is not reflected in terms of temperature increase. This hidden heat is called as latent heat.

The temperature remains constant till the phase change is complete.