2nd Law of Thermodynamics

Question 1

equation for coefficient of performance

Answer 1

= Q/W
= Q/ Qc- Qh
Q = useful heat supplied or rejected
Qc = heat rejected
Qh = heat supplied

Question 2

what does the 2nd law show us about storing energy

Answer 2

that heat can’t be completely converted to work, but work can be completely converted to heat. therefore work is more valuable for storing energy

Question 3

explain the 2nd law of thermodynamics

Answer 3

• it’s not possible to transfer heat from a cooler body to a hotter one without work being done on the system
• some heat must always be rejected during a cycle (net work < heat supplied)

Question 4

requirements for a cycle to be reversible

Answer 4

• heat transfer and work transfer to surroundings must be infinitesimally small

Question 5

Calculate the efficiency of a heat engine

Answer 5

W = ΔQ

η = Δ(Q1 - Q2)/ Q1