Answer:

Heat is energy transferred due to temperature differences only.

Heat transfer can alter system states;

Bodies don't ``contain'' heat; heat is identified as it comes across system boundaries;

The amount of heat needed to go from one state to another is path dependent;

Adiabatic processes are ones in which no heat is transferred.

1.3.2 Zeroth Law of Thermodynamics

With the material we have discussed so far, we are now in a position to describe the Zeroth Law. Like the other laws of thermodynamics we will see, the Zeroth Law is based on observation. We start with two such observations:

If two bodies are in contact through a thermally-conducting boundary for a sufficiently long time, no further observable changes take place; thermal equilibrium is said to prevail.

Two systems which are individually in thermal equilibrium with a third are in thermal equilibrium with each other; all three systems have the same value of the property called temperature.

These closely connected ideas of temperature and thermal equilibrium are expressed formally in the ``Zeroth Law of Thermodynamics:''

Zeroth Law: There exists for every thermodynamic system in equilibrium a property called temperature. Equality of temperature is a necessary and sufficient condition for thermal equilibrium.

The Zeroth Law thus defines a property (temperature) and describes its behavior1.3.

Note that this law is true regardless of how we measure the property temperature. (Other relationships we work with will typically require an absolute scale, so in these notes we use either the Kelvin $ K = 273.15+ ^\circ C$ or Rankine $ R = 459.9 + ^\circ F$ scales. Temperature scales will be discussed further in Section 6.2.) The zeroth law is depicted schematically in Figure 1.8.

Figure 1.8: The zeroth law schematically

Image fig2ThermometerEquilibrium_web

1.3.3 Work

[VW, S & B: 4.1-4.6]

Section 1.3.1 stated that heat is a way of changing the energy of a system by virtue of a temperature DIFFERENCE only. Any other means for changing the energy of a system is called work. We can have push-pull work (e.g. in a piston-cylinder, lifting a WEIGHT), electric and magnetic work (e.g. an electric motor), chemical work, surface tension work, elastic work, etc. In defining work, we FOCUS on the effects that the system (e.g. an ENGINE) has on its surroundings. Thus we define work as being positive when the system does work on the surroundings (energy leaves the system). If work is done on the system (energy added to the system), the work is negative.

Consider a simple compressible substance, for example, a gas (the system), exerting a force on the surroundings via a piston, which moves through some distance, $ l$ (Figure 1.9). The work done on the surroundings, $ W_{\textrm{on surr.}}$ , is

$\displaystyle dW_{\textrm{on surr.}}$ $\displaystyle = \textrm{Force on surr.} \times dl$    

$\displaystyle dW_{\textrm{on surr.}}$ $\displaystyle = \frac{\textrm{Force on surr.}}{\textrm{Area}}\times (\textrm{Area} \times dl)$    

$\displaystyle dW_{\textrm{on surr.}}$ $\displaystyle = \textrm{pressure of surr.} \times d\textrm{Volume}$    

$\displaystyle dW_{\textrm{on surr.}}$ $\displaystyle = p_x\times dV$    

therefore

Explanation: