6. In compressing a system at constant pressure, the work done on the system is
ID: 693298 • Letter: 6
Question
6. In compressing a system at constant pressure, the work done on the system is P times AV, where AV -Vfinal -Vntial. In calculating the change in internal energy by using the equation in the model (AE-q+w), should a positive or negative sign be used, i.e. w-p dV or w =-PAV? 7. Why is the heat of a chemical reaction generally expressed as the change in enthalpy? Efinal-Enitial-Eproducts-Ercactants High Energy 8. In which diagram is energy lost to the Initial State surroundings, i.e. energy flows from the system to the surroundings? E nitial 9. What is the sign of AE in system A? Final StateEtal 10. In which diagram is energy gained from the surroundings, i.c. energy flows from the surroundings to the system? Low Energy System A High Energy Final 11. What is the sign of AE in system B? 12. Consider a beaker of ice and water placed in a State Etoa warm kitchen. What happens? Which diagram,A or B, expresses this system? Explain. Initial State Low EnergY System B 13. Consider a pot of hot water cooling down in the same kitchen What happens? Which diagram, A or B, expresses this system? Explain. sign of w is by system sign of q is If work, w + or -? is done the system by to + or-? +or- If heat, q,IS absorbed released 284Explanation / Answer
6. Considering an adiabatic system (q = 0), change in internal energy should be positive as work is done on the system & not by the system
7. Heat of a reaction is calculated by change in enthapy as enthalpy of formation of products minus entalpy of formation of reactants can give us net heat absorbed by the system (+ve) or heat released by the system (-).
8. In system A as energy of products (final state) is lower than that of reactants (initial state), extra energy is relaese in form of heat.
9. -ve as Efinal is < Einitial, Del E = Efinal - Einitial = -ve
10. System B as energy of products (final state) is greater than that of reactants (initial state), energy flows from surroundings to the system.
11. +ve as Efinal is > Einitial, Del E = Efinal - Einitial = -ve
12. System B. Energy in form of heat flows from surroundings to the system to raise the temperature of beaker having ice.
13. System A as energy in form of heat flows from the system to surroundings to lower the temperature of beaker having ice.
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