Heat and Work

Key Questions

• Question #de1f3

  Heat and work make me think of thermodynamics.
  1) The first law of thermodynamics relates heat Q and work W to the variation of internal energy:
  
  This law says that the internal energy of a body (the sum of ALL the energies, kinetic and potential, of all the particles of the body) can change only when you exchange heat or work with the body.
  For example:
  You can increase the internal energy of a metal block by lighting a fire underneath (heat) or beating it with a hammer (work).
  You can "see" the increase of internal energy because the temperature of the metal block (that is the macroscopic telltale of internal energy) increases.

  A great example of this situation is the Joule's Experiment using the calorimeter and falling weight!!!!

  2) The second law of thermodynamics also relates heat and work introducing the impossibility to convert completely heat into work using a heat machine, as in the next figure:
  
  Consider a steam engine. It takes heat Q1 and converts some of it into work BUT it also releases part of the absorbed heat into the atmosphere (Q2)!!!
  So, the efficiency will be always less than 1 (meaning that you cannot convert 100% of heat into work)!!!

  Gió · 1 · Dec 15 2014

• How does heat energy affect the movement of water molecules?
• How does heat affect the movement of molecules?
• What is thermodynamics equilibrium?
• How can heat cause motion in a liquid?
• Is heat transferred in our atmosphere by conduction?
• How is heat energy transferred?
• How are energy heat and work related?
• How does heat affect resistance?
• How does heat affect pressure?
• In the morning, a concrete statue of specific heat = 600 j/(kg k) has a temperature of 15°c. during the day, it sits in the sun and warms up to 40°c, gaining 90,000 j of thermal energy. what is its mass?
• The temperature of a block of iron, which has a specific heat of 450 j/(kg k), increases by 3 k when 2700 j of energy are added to it. what is the mass of this block of iron?
• How much energy is needed to heat 1 kg of sand, which has a specific heat of 664 j/(kg k) from 30°c to 50°c?
• A substance with a mass of 10 kg gains 106.5 kj of heat when its temperature increases 15°c. what is this substance's specific heat?
• How does heat affect a chemical reaction?
• How is heat transferred in the troposphere?
• What are some common mistakes students make with heat in thermodynamics?
• What is an example of heat in a thermodynamic practice problem?
• Question #cc5ce
• Question #5f3ca
• Question #487bc
• A system performs 354 J of work on its surroundings while losing 133 J of internal energy. How would you determine the heat transferred to the system during this process?
• What is the change in internal energy (in J) of a system that absorbs 0.464 kJ of heat from its surroundings and has 0.630 kcal of work done on it?
• If a system loses 250 kJ of heat at the same time that it is doing 500 kJ of work on the surroundings, what is the change in the internal energy of the system?
• A system receives 525 J of heat and delivers 525 J of work to its surroundings. What is the change in internal energy of the system?
• A gas expands in volume from 35.6 mL to 70.6 mL at constant temperature. What is the work done (in joules) if the gas expands against a constant pressure of 3.2 atm?
• One #"mol"# of an ideal gas, initially at #"300 K"#, is cooled at constant #"V"# so that #"P"_f# is #1/4 "P"_i#. Then the gas expands at constant #"P"# until it reaches #"T"_i# again. What is the work #w# done on the gas?
• A gas is contained in a cylinder with a pressure of 120kPa and is initial volume of 0.66. How much work is done by the gas as it expands at constant pressure to twice its volume, or is compressed to one-third its initial volume?
• One mole of an ideal gas does 3000 J of work on its surroundings as it expands isothermally to a final pressure of 1.00 atm and volume of 250 L. What is the initial volume and the temperature of the gas?
• For a #"313 g"# sample of helium gas that cools by #41.6^@ "C"# due to being compressed by #"267 L"# at a constant external pressure of #"1 atm"#, if its molar heat capacity is #"20.8 J/mol"^@ "C"#, calculate #DeltaE#, #q#, #w#, and #DeltaH#?
• Question #f4ea2
• Question #779d2
• A sample of oxygen gas expands in volume from 1.6 L to 5.4 L at constant temperature. What is the work done in joules if the gas expands against a constant pressure of 0.80 atm?
• What is the work for the free expansion of a gas into vacuum?
• Question #c4236
• Question #1d203
• A steam engine receives 300 kJ of heat from its environment and does 400 kJ of work. How much does the energy of the steam engine change?
• Question #507ad
• During an isothermal process, 5.0 J of heat is removed from an ideal gas. What is the work done in the process?
• How would you calculate the work associated with the compression of a gas from 121.0 L to 80.0 L at a pressure of 13.1 atm?
• Why does more heat transfer take place in a reversible process than in a irreversible process?
• Light with a frequency of #2.79 * 10^15 Hz# strikes a metal surface and ejects electrons that have a maximum kinetic energy of #6.4 eV#. What is the work function of metal?
• Question #b4e89
• Question #f4070
• Question #089c7
• Question #6d1b7
• If for an ideal gas its volume is compressed by a factor of 3, and the gas has cooled down as a result, by what factor is the pressure changed?
• Question #becad
• Question #f4956
• Question #9a548
• Question #5ee30
• Question #3bd67
• If heat goes into a liquid, do I need to care about the work done on the liquid? Aren't they incompressible?
• If a process is taking place at constant temperature and pressure, delta E=0 but what about delta H?
• If the burning of the fuel in a potato cannon performs 855 J of work on the potato and produces 1422 J of heat, what is #DeltaE# for the burning of the fuel?
• Question #f5afc
• Question #d0725
• Question #091d3
• What are values of ΔH, ΔU, ΔS for 1 mole of H20?
• Why is Q = ∆U (heat = change in thermal energy)?
• Question #98403
• Question #c2235
• What is the work done when a sample of gas expands from 12.5L to 17.2L against a pressure of 1.29 atm? Give your answer in Joules.
• Question #d6640
• Question #d1389
• Question #ecbbb
• A piece of metal floats on mercury .the coefficient of expansion of metal and mercury are #gamma_1# and #gamma_2# ,respectively .if the temperature of both metal and mercury increased by an amount #Delta T# . See description ?
• Question #9da59