Heat required to increases the temperature of `1kg` water by `20^(@)C`

Explanation

Heat required `=Delta Q = ms Delta theta`
`=1xx20=20` Kcal.
`therefore S=1 "cal/gm"^@ C=1 "Kcal/kg"^@ C`
Important Points :
(a) We know, `s=(Q)/(m Delta T)`, if the substance undergoes the change of state occurs at constant temperature is infinite.
(b) If the temperature of the substance changes without the transfer of heat `(Q=0)` then `s=(Q)/(m Delta T)=0`. Thus when liquid in the thermos flask is shaken, its temperature increases without the transfer of heat and hence and the specific heat of liquid in the thermos flask is zero.
(c ) To raise the temperature of saturated water vapour, heat (Q) is withdrawn. Hence, specific heat of saturated water vapour is negative. (This is for your information only and not in the course)
(d) The slight variation of specific heat of water with temperature is shown in the graph at 1 atmosphere pressure. Its variation is less than 1% over the interval form 0 to 100°C.