Heat, temperature, heat transfer, 1 st Law of Thermodynamics Thursday, January 28, 2015

Thursday, 1/28  Respond to the following on your weekly warm-up sheet: 1. What is kinetic energy? 2. What variable in the equation KE=1/2mV 2 will increase the kinetic energy of an object? Upcoming dates:  Wednesday, 2/3 – Thermodynamics quiz  Wednesday, 2/3 – Thermodynamics project due  Friday, 2/5 – Thermodynamics test and missing work deadline  Tuesday, 2/16 – Electricity quiz  Wednesday, 2/24 – Electricity quiz  Friday, 2/26 – Electricity Test and missing work deadline  Thursday, 3/3 – Magnetism quiz  Friday, 3/4 – 3NWS Extra credit due by 4:00 PM  Wednesday, 3/9 – Magnetism test  Friday, 3/11 – End of the 3NWS

Heat, temperature, and equilibrium – 7 minutes  Go to today’s resources on my webpage and click on ‘heat and temperature notes’  Use the following questions to guide your notes.  What is heat?  How does heat flow?  What is temperature?  What happens at when a substance reaches equilibrium?  Complete the ‘check your understanding’ questions at the end of the notes.

Review notes

 Heat  Transfer of energy (macroscopic level)  Changes the average kinetic energy of particles (particulate level).  Energy transfers from higher temperature to lower temperatures.  An object decreases its temperature by releasing energy in the form of heat to its surroundings.  An object increases its temperature by gaining energy in the form of heat from its surroundings.

 Temperature  Measures the ability of substance/physical system to transfer energy to another substance/physical system.  Is a measure of kinetic energy of the molecules which make up a substance.  The temperature of a substance will increase/decrease if the average kinetic energy of its particles is increased/decreased.  The higher the temperature transfer heat  The lower the temperature receive heat

 Equilibrium point  As long as there is a difference in temperature between the system and surroundings, heat will be transferred.  When the temperature difference between the system and surroundings is zero the system and surroundings have reached equilibrium.

Check your understanding

How is heat transferred?  Three methods of heat transfer  Convection  Conduction  Radiation  You will work in pairs and do the following:  Visit the resource links to my webpage  Review the documents and take personal notes as applicable.  Search the web for diagrams, pictures, photos, videos of the three forms of heat transfer.  Complete the summary form(one per person).

Heat Transfer Summary Sheet  You will have 20 minutes to complete the summary sheet.  When you have finished turn it into the black tray.

First and Second Laws of Thermodynamics – 5 minutes  Go to today’s resources on my webpage and click on ‘Laws of Thermodynamics notes’  Use the following questions to guide your notes.  What is Internal Energy?  What is the first law of thermodynamics?  What is a reversible and irreversible process?  What is the second law of thermodynamics?  Complete the ‘check your understanding’ questions at the end of the notes.

First Law of Thermodynamics  Energy can be changed from one form to another, but it cannot be created or destroyed.  The total amount of energy and matter in the Universe remains constant, merely changing from one form to another.  The First Law of Thermodynamics (Conservation) states that energy is always conserved, it cannot be created or destroyed. In essence, energy can be converted from one form into another.

Processes in nature Types of processes  Reversible – is a process that after it’s finished can go backwards and end up where it started.  Irreversible – is a process that cannot go back and restore itself  All processes that occur in nature are irreversible (ex. a flower pot is dropped and shatters on the ground – the pot cannot be restored to it’s original state on its own).

Entropy  Is a measure of disorder of a system ‪ Diagram source cnx.orgcnx.org

Entropy  Relating entropy to different states of matter  When a substance is in a gas stage there’s more disorder than there is in a liquid stage because the molecules are held closer together in a liquid form.  When a substance is in a liquid stage there’s more disorder than there is in a solid stage because the molecules are held closer together in a solid stage. ‪ Diagram sources www2.ucdsb.on.ca ‪ Diagram sources www2.ucdsb.on.ca and ‪ cnx.org ‪ cnx.org

Restating the 2 nd Law of Thermodynamics  Natural processes tend to move toward a state of greater entropy.

Cool Down Do you think all substances/objects gain and lose heat at the same rate? Explain your position.

Share your cool down Do you think all substances/objects gain and lose heat at the same rate? Tell your elbow partner your thoughts and explain your position.

What is specific heat?  Every substance gains or loses heat based on its identity/physical property.  The physical property of a substance is its specific heat capacity.

Examples of specific heat

What is specific heat capacity?  Is the amount of heat (thermal energy) required to raise a unit of mass of the substance by one degree of temperature (liquids and solids).  Measure of how much thermal energy is required to change the temperature of a substance.

What is the equation for calculating heat change

How do you determine if heat is gained or lost  If heat energy is gained Q is positive.  If heat energy is lost Q is negative.

Example problem

Practice Problems