 # Why does the temperature remain unchanged until the entire solid changes into liquid

1. Why does the temperature remain unchanged until the entire solid changes into liquid or entire liquid changes into gas even if we are heating the solid or liquid?
2. Convert the following:
• 200°C to the Kelvin scale
• 450K to the Celcius scale
1. Heat is supplied which is used to overcome the forces of attraction between the molecules of solid or liquid. Due to this reason, there is no increase in temperature during the change of state. Hence, temperature remains constant during state change or phase change and this heat used in state change is known as latent heat of fusion and latent heat of vaporisation, respectively. (2)
• We know that, temperature on Kelvin scale
= Temperature on Celsius scale +273.16
= 200 + 273.16= 473.16 K
Thus, a temperature of 200°C on Celsius scale is equal to 473.16 K on the Kelvin scale,
• We know that, temperature on Celsius scale
= Temperature on Kelvin scale -273.16 = 450-273.16
= 176.84° C
Thus, a temperature of 450 K on Kelvin scale is equal to 176.84°C on the Celsius scale.