Question

The standard enthalpies of formation for solid sodium carbonate, aqueous sodium ion, aqueous carbonate ion, and liquid water are -1131 kJ, -240.1 kJ, -677.1 kJ, and -285.8 kJ, respectively. If 5.00 g of solid sodium carbonate at 25.0°C is dissolved in 50.0 g of liquid water, also initially at 25.0°C, immediately after dissolution is complete will the temperature of the resultant solution be greater than, less than, equal to, or cannot be determined compared with 25.0°C? Justify your choice.

Answer 1

The temperature of the resultant sodium carbonate solution will be greater than 25°C

Heat solution of 10℅ sodium carbonate solution is -23.1KJ/mol

For 5 g it is(- 23.1 KJ/106gg)×5 = -1.09 KJ

Heat capacity of water is 4.184J/g°C

50g water will raise the temperature for 1090/(4.184×50)=5.21°C

So, after dissolution the temperature will be 30.21°C