Mixing 50.0 mL of 1.00 M HCl with 50.0 mL of 1.00 M NaOH at 22.0 degrees C raises the temperature to 28.9 degrees C. What is the heat of reaction?

1. Treat the mixed solution as water, with density about 1.0 g/mL. 2. The combined volume is 100.0 mL, so the mass is about 1.0 times ten squared grams. 3. The temperature change is 28.9 minus 22.0, which is 6.9 degrees Celsius. 4. Heat gained by the solution is 4.184 times 100 times 6.9, which is about 2.9 times ten cubed joules. 5. The reaction heat equals minus the solution heat, so it is about minus 2.9 times ten cubed joules. 6. The negative sign shows the reaction released heat, so it is exothermic. 7. Halving the mass to 50.0 g would give the 1.4 times ten cubed trap, but both solutions absorb the heat. _Source: OpenStax Chemistry (CC BY 4.0), Ch 5 "Thermochemistry", section 5.2 Calorimetry_