Portage Chemistry 103 Module 3 Exam Study Detailed answers with Rationale.

Portage Chemistry 103 Module 3 Exam
Study Detailed answers with Rationale.
Portage Chemistry 103 Module 3 Exam
Study Detailed answers with Rationale.
3.1: THERMOCHEMISTRY - ANSWER Thermodynamics is the study of the relationship between heat and
other forms of energy, particularly mechanical work. Thermochemistry is the part of thermodynamics
that deals with the quantity of heat given off or absorbed during a chemical reaction. The quantity of
heat given off or absorbed during a physical change or temperature change can also be studied, and we
will refer to this process as calorimetry.



System - ANSWER the object (or substance) being studied



Open system - ANSWER a system that permits the transfer of mass and energy with the surroundings



Closed system - ANSWER a system that permits the transfer of energy but not mass with the
surroundings



Isolated system - ANSWER a system that does not permit the transfer of energy or mass with the
surroundings



Surroundings - ANSWER the rest of the universe interacting with the system



Energy - ANSWER the potential or capacity to move matter: the ability to do work (unit is J = joule)



Work - ANSWER the amount of energy transferred by a force acting through a distance



Kinetic energy - ANSWER the energy possessed by an object by virtue of its motion (unit is J = joule)



Potential energy - ANSWER the energy possessed by an object by virtue of its position (unit is J = joule)

,Portage Chemistry 103 Module 3 Exam
Study Detailed answers with Rationale.
Heat (q) - ANSWER the thermal energy transferred between system and surroundings due to a
difference in temperature between them (unit is J = joule)



Enthalpy - ANSWER the total energy of a system



Heat of reaction - ANSWER (ΔH) the amount of heat (q) gained or lost during a chemical reaction



Exothermic - ANSWER a reaction with a - ΔH



Endothermic - ANSWER a reaction with a + ΔH (absorb heat)



Calorimetry - ANSWER The energy change that accompanies a physical, temperature, or chemical
change is determined by carrying out the process in a device known as a calorimeter. The calorimeter is
able to measure the amount of heat absorbed or evolved as a process takes place. A styrofoam coffee
cup calorimeter can be used to measure an energy change that takes place at constant pressure. An
enclosed bomb calorimeter is used to measure an energy change that takes place at constant volume
with a change in pressure.



Temperature change calorimetry - ANSWER measures the thermal energy change occurring as a system
at higher temperature transfers kinetic energy to a system at lower temperature, which is reflected by a
change in temperature for the overall system. This is demonstrated below by adding a 15.6 gram piece
of aluminum (heated to 100oC) to a 45.6 gram sample of water at 26.7oC in a coffee cup calorimeter.
The final temperature of this system can be predicted using the equations below and several facts about
the materials (Al and H2O).

Heat temp change = qtemp change = mass x specific heat (heat capacity) x temp change = m x c x ∆t



(mAl x cAl x ∆tAl) = (mH2O x cH2O x ∆tH2O)



However, since the Al is losing heat, we'll use a negative sign in front of the heat loss equation.



- (mAl x cAl x ∆tAl) = (mH2O x cH2O x ∆tH2O)

, Portage Chemistry 103 Module 3 Exam
Study Detailed answers with Rationale.

We know ∆t = Tempmixture - Tempinitial, so we can substitute the data to get:

- [15.6 g x 0.899 J/g oC x (Tmix - 100oC)] = [(45.6 g x 4.184 J/g oC x (Tmix - 26.70oC)]



Now, solve:

- [14.0244 J/oC x (Tmix - 100oC)] = [(190.7904 J/oC x (Tmix - 26.7oC)]

- 14.0244 Tmix + 1402.44 = 190.79 Tmix - 5094.1

6496.44 = 204.8144 Tmix

Tmix = 6496..8144 = 31.7oC



Phase change calorimetry - ANSWER measures the energy change occurring as a substance changes
from one phase (state) to another, such as water melting or boiling, or ice freezing or steam condensing.
In this case, no temperature change occurs, but the energy change causes the particles of the substance
to form or break intermolecular bonds and change from one state to another. The equations used to do
phase change calorimetry calculations are shown below:



Phase changes of solid to liquid or liquid to solid:

qs↔i = mass x Heat of Fusion = m x ∆Hfusion



Phase Changes of liquid to gas or gas to liquid:

ql↔g = mass x Heat of Vaporization = m x ∆Hvapor



What is the energy involved in vaporization of 200 grams of water at 100oC if the heat of vaporization
for water is 2.26 kJ/g? - ANSWER When energy is given off in any of these phase changes, a negative sign
is placed in front of the value, and when energy is added, a positive sign is placed in front of the value.

ql↔g = m x ∆Hvapor = 200 g x 2.26 kJ/g = 452 kJ (since heat is added) = + 452 kJ



What is the energy involved in freezing 200 grams of water at 0oC if the heat of fusion for water is 0.334
kJ/g? - ANSWER ql↔s = m x ∆Hfusion = 200 g x 0.334 kJ/g = 66.8 kJ (since heat is removed/given off) = -
66.8 kJ