100g of water is heated from `30^@C to 50^@C`. Ignoring the slight expansion of the water, the change in its internal energy is (specific heat of water is `4184J//kg//K`):

Options

A. `4.2 kJ`
B. `8.4 kJ`
C. `84 kJ`
D. `2.1 kJ`

Answer

B

Explanation

`DeltaQ = M, S, DeltaT`
`= 100 xx 10^(-3) xx 4.184 xx 20`
`= 8.4 xx 10^(3)`
`DeltaQ = 8.4 kJ, DeltaW = 0`
`DeltaQ = Deltau +DeltaW`
`:. Deltau = 8.4 kJ`.