In this experiment we will use the equation of state a balloon and liquid

# In this experiment we will use the equation of state

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where n is the number of moles of a substance. In this experiment we will use the equation of state, a balloon and liquid nitrogen to estimate the value of absolute zero. The first law of thermodynamics is one of the most important laws of physics. First it is important to make a distinction between internal energy and heat . Internal energy is all of the energy of a system associated with its microscopic components (when viewed from a reference frame as rest with respect to the center of mass.) Heat is defined as the transfer of energy across the boundary of the system due to a temperature difference between the system and its surroundings. Heat and work are ways of changing the energy of a system. The first law of thermodynamics is a special case of the law of conservation of energy that describes
processes in which only the internal energy internal energy ! E int changes and the only energy transfers are by heat Q and work W: ! E int = Q + W Equation 2 Internal energy is a state variable like pressure, volume and temperature. An adiabatic process is one in which no energy leaves of enters the system by heat (i.e., Q= 0.) This can be achieved by either insulating the walls of the container or by performing the process rapidly so that there is negligible time for energy to transfer by heat. Thus Equation 2 becomes ! E int = W (adiabatic process) Equation 3 This shows that if a gas is compressed adiabatically, such that W is positive then ! E int is positive and the temperature of the gas increases. This is how a diesel engine combusts the fuel air mixture while using no spark plugs. A process that occurs at constant temperature is called an isothermal process . A plot of P vs. V at constant temperature for an ideal gas yields a hyperbolic curve called an isotherm. The internal energy of an ideal gas is a function of temperature only. Thus ! E int = 0 and we can conclude that for an isothermal process the energy transfer Q must be equal to the negative of the work done on the gas, i.e., Q = ! W . Any energy that enters the system is transferred out of the system by work resulting in ! E int = 0 . As noted above an adiabatic process is one in which no energy is transferred between a system and its surroundings. The diesel is one example and another is the slow expansion of a gas that is thermally insulated from its surroundings. All three variables in the ideal gas law (P, V and T) change during an adiabatic process. For an adiabatic process undergoing infinitesimal changes in volume dV and temperature dT , the first law of thermodynamics can be used to obtain the following relationships.

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