15. How much heat energy (in kJ) is evolved by a reaction in a bomb calorimeter in which the temperature of the bomb and water increased from 19.5 to 22.83 ºC? The bomb has a heat capacity of 650 J/C; the calorimeter contains 320 g of water.
q = [mass H2O x specific heat H2O x (Tfinal-Tinitial)] + [Ccal*(Tfinal-Tintiial)]
Substitute and solve for q, then convert to kJ.
To calculate the heat energy evolved by the reaction, we can use the formula:
Heat energy (Q) = Heat capacity (C) * Change in temperature (ΔT)
First, let's calculate the change in temperature (ΔT):
ΔT = Final temperature - Initial temperature
ΔT = 22.83 ºC - 19.5 ºC
ΔT = 3.33 ºC
Next, let's convert the mass of water to kilograms, as the heat capacity is given in J/ºC:
Mass of water = 320 g
Mass of water = 320 g / 1000
Mass of water = 0.32 kg
Now, we can calculate the heat energy (Q) using the formula:
Q = C * ΔT
Plugging in the values:
Q = 650 J/ºC * 3.33 ºC
Q = 2164.5 J
To convert the heat energy from joules (J) to kilojoules (kJ), divide by 1000:
Q (in kJ) = 2164.5 J / 1000
Q (in kJ) = 2.1645 kJ
Therefore, the heat energy evolved by the reaction in the bomb calorimeter is 2.1645 kJ.