Thermochem

Objectives Today I will be able to: Diagram the heat transfer between the systems and surroundings for reactions Calculate the energy absorbed or released during heat transfer Informal assessment – monitoring student interactions and questions as we complete the notes and the polls Formal assessment – analyzing student responses to the polls and practice problems

Lesson Sequence Evaluate: Warm Up Explain: Thermochemistry Notes Evaluate: Closure

Warm Up What is the difference between potential energy and kinetic energy? What is the difference between temperature and heat? What is the difference between endothermic and exothermic reactions? Note: It is incorrect to say that an object contains a certain amount of heat… “heat exchange or transfer” is correct terminology

Objectives Today I will be able to: Diagram the heat transfer between the systems and surroundings for reactions Calculate the energy absorbed or released during heat transfer

Homework Organic Functional Groups Quiz Friday, September 26 Bring your textbook to exchange!

Agenda Warm – Up Thermochemistry Notes Closure

Thermochemistry (Chapter 5)

First Law of Thermodynamics Energy cannot be created or destroyed Energy is conserved

System vs. Surroundings System – all of the substances undergoing a physical or chemical change Surroundings everything that is not apart of the system Open, closed, isolated

A Piston is an Example of a Closed System http://www.learnthermo.com/images/ch01/Lesson-C/piston-cylinder.png

https://www.polleverywhere.com/multiple_choice_polls/vZj7hr1dKpGhZbU

Heat transfer occurs until a thermal equilibrium is reached smithplanet.com

Internal Energy (E) Sum of all the kinetic and potential energies of the components of the system our focus is typically the change in energy (ΔE) ΔE = Efinal - Einitial

An increase of internal energy typically occurs when Temperature increases A phase change occurs A chemical reaction initiates

https://www.polleverywhere.com/multiple_choice_polls/SOCITqmu8Q2zN5t

Energy Diagram

Energy diagram of water wps.prenhall.com

Determine the direction of energy transfer in the diagram

https://www.polleverywhere.com/multiple_choice_polls/W6DACqyLtZapeub

The internal energy of Mg(s) and Cl2(g) is greater than that of MgCl2(s). Sketch an energy diagram that represents the reaction MgCl2(s)  Mg(s) + Cl2(g)

Energy in a system comes from two places: HEAT WORK Energy used to cause the temperature of an object to increase Energy used to cause an object to move NOTES: THE FIRST LAW ENDS

ΔE = q + w

Practice Problem 1 Gases A(g) and B(g) are confined in a cylinder-and-piston arrangement and react to form a solid product C(s): A(g) + B(g)  C(s). As the reaction occurs the system loses 1150 J of heat to the surroundings. The piston moves downward as the gases react to form a solid. As the volume of the gas decreases under constant pressure of the atmosphere, the surroundings do 480 J of work on the system. What is the change in internal energy of the system?

Answer ΔE = q + w q = -1150 J w= + 480J ΔE = q + w = (-1150 J)+(480 J) = -670 J Tells us the net value of energy transferred from the system to the surroundings was 670 J.

Practice Problem 2: You try Calculate the change in the internal energy for a process in which a system absorbs 140 J of heat from the surroundings and does 85 J of work on the surroundings

https://www.polleverywhere.com/multiple_choice_polls/Z0ZIfqWgZvChrdd

Closure Complete the practice problems 5.3, 5.4, 5.7,5.25 Reread section 5.3 and 5.4 about enthalpy