Chapter 7: Hot & Cold Packs Introductory Activity How many things can you think of in everday life that either give off heat or absorb heat? Which of these things are physical processes? Which are chemical processes? Hot & Cold Packs This
chapter will introduce the chemistry needed to understand how Hot & Cold Packs work Section 7.1: Endothermic & Exothermic Section 7.2: Calorimetry and heat capacity Section 7.3: Changes in State Section 7.4: Heat of a Chemical Reaction Section 7.5: Hesss Law Hot/Cold Packs Use
Transfer Transferof of energy energy between System System&& Surroundings Surroundings Is determined with
Calorimetry Calorimetry Physical Physical change change Can be done in Effect on temperature depends on Chemical Chemical
change change Materials Materialsability abilityto to absorb absorbenergy energy without withoutnoticeable noticeable temperature
temperature change change Section 7.1Endothermic and Exothermic Why are hot packs hot and cold packs feel cold Endothermic & Exothermic When the system absorbs energy from the surroundings, its an endothermic process
When the system releases energy to the surroundings, its an exothermic process System & Surroundings Its very important to define the system & surroundings correctly to use the endoand exothermic definitions! Most people define the system too broadly They include everything in the beaker or container as the system
However, the system is only the molecules undergoing the change System & Surroundings The system is only made of the molecules undergoing the change The water molecules & the container Your hand and the air Even the thermometer They are all the surroundings Note that water is made up of water molecules
not a solid chunk of waterbut for this picture, its best to represent water as one thing since its the surroundings and focus on the molecules reacting as the system. Exothermic & You You touch the beaker and it feels hot Energy is being transferred TO YOU You are the surroundings When energy moves from system to surroundings, its exothermic Exothermic & the Thermometer
The temperature (measured by the thermometer) is related to the average kinetic energy of the molecules in the container The majority of the molecules in a solution are water If the temperature is increasing, the energy of the water molecules is increasing Since water is the surrounding (its not actually reacting), energy is being transferred to the surroundings Exothermic shows an increase in the temperature within the container
Endothermic The opposite is also true If the container feels cold to you, energy is being transferred FROM YOU (the surroundings) into the system endothermic If the thermometer goes down, energy is being transferred FROM the water molecules (surroundings) into the system-endothermic Lets Practice
Example: Identify the system and surroundings when you hold an ice cube while it melts. Is this endoor exothermic? Lets Practice Example: Identify the system and surroundings when you hold an ice cube while it
melts. Is this endoor exothermic? System: Water molecules in the form of ice Surroundings: You and the air It feels cold to youso energy is leaving you (surroundings) When energy goes from surroundings to system its endothermic
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This led to anger in Britain. They demanded that Mason and Slidell be released and the Union must made a public apology. They also prepared a fleet for action and soldiers were sent to Canada. They also stopped the export...
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