Work is taken negative when the work is done by the system and heat is taken as positive when it is transferred into the system. （ ）
举一反三
- Work is（ ）when energy is removed from the system. A: positive B: negative C: down D: Not sure
- DU = 100 J is for a system that gives off 100 J of heat and ( ) A: does no work B: does 200 J of work C: has 100 J of work done on it D: has 200 J of work done on it.
- When a system moves from A state along path I to B state, it releases heat of 100 J and obtains 50 J work at the same time; when the system does 80J work from A state along path Ⅱ to B state, then Q is（ ） A: 70J B: 30J C: －30J D: －70J
- For a system of an ideal gas, in which process of the following that the heat absorbed by the system and the work done toward the surroundings are positive? A: Isochoric (等体) and pressure decreasing process. B: Isothermal (等温) and expanding process. C: Adiabatic and expanding process. D: Isobaric (等压) and compressed process
- A control volume is: （ ） A: An isolated system B: A closed system but heat and work can cross the boundary C: A specific amount of mass in space D: A fixed region in space where mass, heat and work can cross the boundary of that region