When 100 mL of 0.200 M NaCl (aq) and 100 mL of 0.200 M AgNO3 (aq), both at 21.9 °C, are mixed in a coffee cup calorimeter, the temperature increases to 23.5 °C as solid AgCl forms. How much heat is produced by this precipitation reaction? What assumptions did you make to determine your value?

There is 1.3 kJ heat produced (released)

Explanation:

Step 1: Data given

Volume of a 0.200 M Nacl solution = 100 mL = 0.1 L

Volume of a 0.200 M AgNO3 solution = 100 mL = 0.1 L

Initial temperature = 21.9 °C

Final temperature = 23.5 °C

Solid AgCl will be formed

Step 2: The balanced equation:

AgNO3 (aq) + NaCl (aq) → AgCl (s) + NaNO3 (aq)

AgCl (s) + NaNO3 (aq) → Na + (aq) + NO3 - (aq) + AgCl (s)

Step 3: Define the formula

Pressure is constant. → the heat evolved from the reaction is equivalent to the enthalpy of reaction.

Q=m*c*ΔT

⇒ Q = the heat transfer (in joule)

⇒ m = the mass (in grams)

⇒ c = the heat capacity (J/g°C)

⇒ ΔT = Change in temperature = T2 - T1

Step 4: Calculate heat

Let's vonsider the density the same as the density of water (1g/mL)

Mass = volume * density

Mass = 200 mL * 1g/mL

Mass = 200 grams

Q = m*c*ΔT

⇒ m = 200 grams

⇒ c = the heat capacity (let's consider the heat capacity of water) = 4.184 J/g°C

⇒ ΔT = 23.5 - 21.9 = 1.6°C

Q = 200 * 4.184 * 1.6 = 1338.9 J = 1.3 kJ

There is 1.3 kJ heat produced (released)

Therefore, we assumed no heat is absorbed by the calorimeter, no heat is exchanged between the calorimeter and its surroundings, and the specific heat and mass of the solution are the same as those for water (1g/mL and 4.184 J/g°C)