Important Notes on 1st Law 1.E is always measured relative to reference point! ··Reference plane for PE 。·Reference frame for KE .Reference state for U (i.e.U=0@reference state) 2.Changes in E are important,not total values of E 3.AE depends only on beginning and end states (property) 4.Q and W depend on process path (could get to the same end state with different combinations of Q and W) 国 5.Energy balance for a particular problem will depend on the system that you select >YOU MUST ALWAYS SPECIFY YOUR SYSTEM IN ORDER TO APPLY THE 1ST LAW 6.Total heat transfer is the summation of all heat transfers across the system boundary Q-∑Q, 7.Total work is the summation of all work transfers across the system boundary W=∑W 上游充通大学 March 7,2019 4 SHANGHAI JLAO TONG UNIVERSITYMarch 7, 2019 4 Important Notes on 1st Law 1. E is always measured relative to reference point! • • Reference plane for PE • • Reference frame for KE • • Reference state for U (i.e. U = 0 @ reference state) 2. Changes in E are important, not total values of E 3. ΔE depends only on beginning and end states (property) 4. Q and W depend on process path (could get to the same end state with different combinations of Q and W) 5. Energy balance for a particular problem will depend on the system that you select YOU MUST ALWAYS SPECIFY YOUR SYSTEM IN ORDER TO APPLY THE 1ST LAW 6. Total heat transfer is the summation of all heat transfers across the system boundary 7. Total work is the summation of all work transfers across the system boundary