Unit 6 Formative Assessment (02-12-24)
Highlighted in yellow means the answer is correct.
1. A student performs a calorimetry experiment to determine the molar enthalpy of solution, ΔHsoln, of lithium
chloride, LiCl. The student places a sample of water into a coffee-cup calorimeter and immerses a
thermometer in the water to record the initial temperature. Then the student adds a sample of LiCl(s) to the
water and stirs the mixture gently until all of the solid dissolves completely. Data from the experiment are
shown in the table below. Assume that the specific heat capacity of the calorimeter is negligible.
At the end of the experiment, the student performed the following calculation to determine the magnitude of
heat absorbed by the solution during the dissolution of LiCl(s).
(a) One of the three numbers used by the student in the calculation shown above is incorrect.
Identify the incorrect number.
The incorrect number is 100.0 g. This value represents the mass of the water only.
The mass of the entire solution should be used in this calculation.
(b) Write the correct value that should be used to replace the incorrect number identified in part (a).
110.0 g
(c) Using the value from part (b), calculate the correct value for the magnitude of heat (q) absorbed by the
solution during the dissolution of LiCl(s). Show your calculations in the space below. Include units in
your answer.
q = mcΔT = ( 110.0 g )( 4.18 J/(g·°C) )( 18.9°C ) = 8690 J = 8.69 × 103 J = 8.69 kJ
, 1. (continued)
(d) Calculate the number of moles of LiCl(s) used in this experiment. Show your calculations in the space
below. Include units in your answer.
(e) Is the dissolution of LiCl classified as an endothermic process or an exothermic process?
Justify your answer using the information in the data table.
The dissolution of LiCl is classified as an exothermic process.
The temperature of the solution increased during the experiment. This means that thermal
energy was released by the system to the surroundings during the dissolution process.
(f) Determine the value of ΔHsoln for LiCl, in units of kJ/mol. Show your calculations in the space below.
Include units in your answer. Include the appropriate algebraic sign with your answer.
The following represents a list of particle-particle interactions that are either broken or formed during the
dissolution of LiCl(s).
Particle-Particle Interactions
Li+ ions and Cl– ions
H2O molecules and H2O molecules
X Li+ ions and H2O molecules
X Cl– ions and H2O molecules
(g) In the table above, place an “X” next to all of the particle-particle interactions that contribute
significantly to the overall energy change that occurred during the dissolution of LiCl(s).
(h) Do the choices that you identified in part (g) represent particle-particle interactions that are broken or
formed during the dissolution of LiCl(s)?
The particle-particle interactions I chose in part (g)
are formed during the dissolution of LiCl(s).
Forming an attractive force is an exothermic process that releases energy.
Highlighted in yellow means the answer is correct.
1. A student performs a calorimetry experiment to determine the molar enthalpy of solution, ΔHsoln, of lithium
chloride, LiCl. The student places a sample of water into a coffee-cup calorimeter and immerses a
thermometer in the water to record the initial temperature. Then the student adds a sample of LiCl(s) to the
water and stirs the mixture gently until all of the solid dissolves completely. Data from the experiment are
shown in the table below. Assume that the specific heat capacity of the calorimeter is negligible.
At the end of the experiment, the student performed the following calculation to determine the magnitude of
heat absorbed by the solution during the dissolution of LiCl(s).
(a) One of the three numbers used by the student in the calculation shown above is incorrect.
Identify the incorrect number.
The incorrect number is 100.0 g. This value represents the mass of the water only.
The mass of the entire solution should be used in this calculation.
(b) Write the correct value that should be used to replace the incorrect number identified in part (a).
110.0 g
(c) Using the value from part (b), calculate the correct value for the magnitude of heat (q) absorbed by the
solution during the dissolution of LiCl(s). Show your calculations in the space below. Include units in
your answer.
q = mcΔT = ( 110.0 g )( 4.18 J/(g·°C) )( 18.9°C ) = 8690 J = 8.69 × 103 J = 8.69 kJ
, 1. (continued)
(d) Calculate the number of moles of LiCl(s) used in this experiment. Show your calculations in the space
below. Include units in your answer.
(e) Is the dissolution of LiCl classified as an endothermic process or an exothermic process?
Justify your answer using the information in the data table.
The dissolution of LiCl is classified as an exothermic process.
The temperature of the solution increased during the experiment. This means that thermal
energy was released by the system to the surroundings during the dissolution process.
(f) Determine the value of ΔHsoln for LiCl, in units of kJ/mol. Show your calculations in the space below.
Include units in your answer. Include the appropriate algebraic sign with your answer.
The following represents a list of particle-particle interactions that are either broken or formed during the
dissolution of LiCl(s).
Particle-Particle Interactions
Li+ ions and Cl– ions
H2O molecules and H2O molecules
X Li+ ions and H2O molecules
X Cl– ions and H2O molecules
(g) In the table above, place an “X” next to all of the particle-particle interactions that contribute
significantly to the overall energy change that occurred during the dissolution of LiCl(s).
(h) Do the choices that you identified in part (g) represent particle-particle interactions that are broken or
formed during the dissolution of LiCl(s)?
The particle-particle interactions I chose in part (g)
are formed during the dissolution of LiCl(s).
Forming an attractive force is an exothermic process that releases energy.
