Thermochemistry 3 Boon Chemistry January 31 and February 1, 2013

Catalyst For the two pictures below, determine the direction of heat flow, the name of the phase change, and whether the process is endothermic or exothermic.  Objectives I can explain specific heat capacity and perform calculations using: Q = m c Δ T  Objectives I can explain specific heat capacity and perform calculations using: Q = m c Δ T  Agenda  Catalyst  States of Matter Review  Notes: Specific Heat  Practice Q = m c Δ T  Exit Slip: Exothermic vs. Endothermic  Agenda  Catalyst  States of Matter Review  Notes: Specific Heat  Practice Q = m c Δ T  Exit Slip: Exothermic vs. Endothermic  Take out your homework please. System1: The water System 2: liquid gold in bar mold

Phase Diagram Review (1) Ice; temperature is increasing (2) Ice and water; temperature is constant (3) water; temperature is increasing (4) Water & steam; temperature is constant (5) steam; temperature is increasing #2: The temperature remains constant when the water is a mixture of ice and water because the energy is being used to melt the ice. #4: When water boils the kinetic energy of molecules increases. The molecules move faster. This is endothermic because it requires energy. #5: When water freezes the kinetic energy of molecules decreases. The molecules move slower. This is exothermic because energy is released.

White Board Practice  (1) When you move from solids to liquid, liquids to gas, what is happening to the individual molecules (what is occurring on a molecular level?)  (2) When you are moving from gases to liquids, liquids to solids, what is happening on a molecular level?   Check out this video. Are these reactions exothermic or endothermic? How do you know?

States of Matter Vocabulary Review:  Use your notes to complete the chart AND bubbles.

Notes: Specific Heat (aka heat capacity or specific heat capacity)  Specific heat is the amount of energy that must be transferred as heat to raise the temperature of 1 gram (g) of a substance by 1 Kelvin (K).   The term used for specific heat is a lowercase “c”. The units for specific heat are Joules/gram*Kelvin or (J/g*K).   Different substances have different specific heats.

Specific Heat Data. Use the table to answer the following questions.  What substance in the table as the highest specific heat?   What substance has the lowest specific heat?   Which substance requires more heat energy to increase its temperature: calcium or gold?   A substance with a high specific heat requires (more/less) heat energy to raise the temperature of a 1 g sample by 1 K than a substance with a low specific heat.

Specific Heat Calculations  If we know the specific heat of a substance, we can calculate the amount of heat energy required to raise the temperature of a sample of a substance by a certain amount.   The formula:

Heat Transfer Calculations  Example 1: A g sample of water was heated and the temperature increased by 10 K. How much heat did the water absorb?

Heat Transfer Calculations  Example 2: A 10.0 g sample of aluminum was heated from 300 K to 325 K. How much heat was absorbed by the aluminum?

Heat Transfer Calculations  Example 3: A 0.5 g platinum ring was dropped in the snow and its temperature dropped from 35 °C to 0 °C. How much heat was released?

Exit Slip  Expectations:  You will work silently and independently.  When you are done, cover your exit slip with your handouts.  Tools:  You may use all your notes, worksheets, and flash cards.  You may use your own calculator.  What do I turn in?  You will turn in your exit slip only.  Homework:  Due Next Class: Read pp. 60 – 61 Do problems p. 61 #1-4; Read pp problems pp. 344 #1, 2, 3, 7, 16  Complete any worksheets or article questions that you have not finished.

Homework  Due Next Class: Read pp. 60 – 61 Do problems p. 61 #1- 4; Read pp problems pp. 344 #1, 2, 3, 7, 16  Due Next Thurs/Fri (Feb. 7 & 8): All Thermochemistry notes and handouts.