Portage Chemistry 103 Module 3 Exam 2023 with 100% correct answers

3.1: THERMOCHEMISTRY 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 the object (or substance) being studied Open system a system that permits the transfer of mass and energy with the surroundings Closed system a system that permits the transfer of energy but not mass with the surroundings Isolated system a system that does not permit the transfer of energy or mass with the surroundings Surroundings the rest of the universe interacting with the system Energy the potential or capacity to move matter: the ability to do work (unit is J = joule) Work the amount of energy transferred by a force acting through a distance Kinetic energy the energy possessed by an object by virtue of its motion (unit is J = joule) Potential energy the energy possessed by an object by virtue of its position (unit is J = joule) Heat (q) the thermal energy transferred between system and surroundings due to a difference in temperature between them (unit is J = joule) Enthalpy the total energy of a system Heat of reaction (ΔH) the amount of heat (q) gained or lost during a chemical reaction Exothermic a reaction with a - ΔH Endothermic a reaction with a + ΔH (absorb heat) Calorimetry 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 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) 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 = 6496.44 / 204.8144 = 31.7oC