Chemistry Question on Thermochemistry?

Density of water = 1.00 g/mL
Mass of water = (675 mL) × (1.00 g/mL) = 675 g
Specific heat capacity of water = 4.184 J/(g°C)

Heat produced by the combustion of TNT sample
= (Heat absorbed by the calorimeter) + (Heat absorbed by the water)
= (534 J/°C) × [(26.9 - 23.4) °C] + (675 g) × [4.184 J/(g°C)] × [(26.9 - 23.4) °C]
= 11800 J (to 3 sig. fig.)
= 11.8 kJ

Let’s determine the increase of the temperature.
∆ T = 26.9 – 23.4 = 3.5˚

For the calorimeter, Q = 534 * 3.5 = 1,869 J

According to a table in my physics book, the specific heat of water is 4,186 J/(kg * ˚C). Since water has density of 1 g/ml, the mass of water is 675 grams. This is 0.675 kg.

Q2 = 0.675 * 4,186 * 3.5 = 9,889.425 J
Total energy = 1,869 + 9,889.425 = 11,758.425 J

If we round to three significant digits, this is 11,800 joules. I hope this is helpful for you.