1a. When a solid dissolves in water, heat may be evolved or absorbed. The heat o
ID: 557289 • Letter: 1
Question
1a. When a solid dissolves in water, heat may be evolved or absorbed. The heat of dissolution(dissolving) can be determined using a coffee cup calorimeter.
1b.
1c.
In the laboratory a "coffee cup" calorimeter, or constant pressure calorimeter, is frequently used to determine the specific heat of a solid, or to measure the energy of a solution phase reaction.
A student heats 64.53 grams of magnesium to 98.68 °C and then drops it into a cup containing 79.69 grams of water at 20.97 °C. She measures the final temperature to be 33.36 °C.
The heat capacity of the calorimeter (sometimes referred to as the calorimeter constant) was determined in a separate experiment to be 1.78 J/°C.
Assuming that no heat is lost to the surroundings calculate the specific heat of magnesium.
Specific Heat (Mg) = J/g°C.
1d.
1e. The standard enthalpy change for the following reaction is 903 kJ at 298 K.
What is the standard enthalpy change for this reaction at 298 K?
___ kJ
1f.
The standard enthalpy change for the following reaction is -116 kJ at 298 K.
What is the standard enthalpy change for the reaction at 298 K?
_____kJ
When a solid dissolves in water, heat may be evolved or absorbed. The heat of dissolution(dissolving) can be determined using a coffee cup calorimeter.In the laboratory a general chemistry student finds that when 10.82 g of NaClO4(s) are dissolved in 101.10 g of water, the temperature of the solution drops from 22.40 to 19.02 °C.
The heat capacity of the calorimeter (sometimes referred to as the calorimeter constant) was determined in a separate experiment to be 1.65 J/°C.
Based on the student's observation, calculate the enthalpy of dissolution of NaClO4(s) in kJ/mol.
Assume the specific heat of the solution is equal to the specific heat of water.
Hdissolution = kJ/mol
Explanation / Answer
Question 1 a
Molar mass: 159.609 g/mol
Q = mcT
Q = heat energy (Joules, J), m = mass of a substance (kg)
c = specific heat (units J/kgK), is a symbol meaning "the change in"
T = change in temperature (Kelvins, K)
Q = 109.2 x 4.184 x (27.61-25.19) = 1105.918 Joules
heat capacity of the calorimeter = 2.42 x 1.72 = 4.1624 Joules
Total heat realesed = 1105.918 + 4.1624 = 1110.0804 Joules
Moles of Copper = 2.38 / 159.609 = 0.0149 Moles
Enthalpy of dissolution of CuSO4(s) = 1110.08.04 / 0.0149 x 1000 =74.502 kj
Question 1c
Heat released by heat = 79.69 x 4.184 x (33.36-20.97) + 1.78 x (33.36-20.97) = 4153.16 Joules
Specific heat of magnesium = 4153.16 joules / (98.68 -33.36) °C x 64.53 g = 0.98 J/g°C
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