Question

In a coffee-cup calorimeter experiment, 10.00 g of a soluble ionic compound was added to the calorimeter contained 75.0 g H2O initially at 23.2°C. The final temperature of the solution was 31.8°C. What was the change in enthalpy for the dissolution of this compound?

Answer 1

The enthalpy for dissolution is - 305.558 J/g

Solution:

Mass of the ionic compound, m = 10.00 g

Mass of water, m' = 75.0 g

Initial temperature, T =
`23.2^(\circ)C`

Final Temperature, T' =
`31.8^(\circ)C`

Now,

To calculate the change in enthalpy:

We know that the specific heat of water is 4.18
`J/g^(\circ)C`

Total mass of the solution, M = m + m' = 10.00 + 75.0 = 85.0 g

Temperature, difference,
`\Delta T = T' - T = 31.8 - 23.2 = 8.6^(\circ)C`

Thus

The heat absorbed by the solution is given by:

`Q = MC_(w)\Delta T = 85.0* 4.18* 8.6 = 3055.58\ J`

Enthalpy,
`\Delta H = -(Q)/(m) = - (3055.58)/(10) = - 305.558\ J/g`