1. LAWS OF THERMODYNAMICS

2. DO NOW – TAKE OUT HW Initial state 1.What did I do when I pushed the plunger down? 2.What is happening to the gas inside? 3.How does the energy of the gas in the final state compare to energy of the gas in the initial state? Final state gas

3. NOTES First Law of Thermodynamics – the change in thermal energy of a system is equal to the sum of heat added and the work done on the system. ΔU = Q + W ΔU = Q - W Thermal Energy or Internal Energy When work is done ON the system When work is done BY the system

4. AN EXTERNAL FORCE DOES 120 J OF WORK AS IT COMPRESSES A PISTON OF GAS. THE THERMAL ENERGY OF THE GAS INCREASES BY 50 J. IS HEAT ABSORBED BY THE GAS OR EMITTED BY THE GAS? HOW MUCH HEAT? ΔU = Q + W 50 J = Q + 120 J Q = 50 J – 120 J Q = -70 J W= 120 J ΔU = 50 J Q = ? work is done ON the system

5. SELF-ASSESSMENT 1 2 3 1I need help with phase change problems 2I could use practice with both phase change and 1 st Law problems 3I want to focus on 1 st Law problems

6. HOMEWORK Finish this worksheet - (Due Friday 3/14)