If we place 0.5 g Lithium metal in coffee cup calorimeter that already contains 75 ml of water. The specific heat capacity of reaction mixture is
`4Jg ^(-1) K ^(-1).` Temperature of water is increased from `22^(@)C `to `72^(@)C.` Then find `Delta ` H for the reaction.
`2 Li (s) + 2 H _(2) O (l) to 2 Li OH (aq) + H _(2) (g)`

Options

A. `-11.2 kJ//mol`
B. `= 16.1 kJ //mol`
C. `-422.8kJ //mol`
D. `-211.4kJ//mol`

Answer

C

Explanation

`Q = ms Delta T = 75.5 xx 4 xx 50 J = 15.1 kJ`
`therefore Delta H = - (15. 10 xx 7)/(0.5) kJ//mol =-422.8kJ//mol`