calculate absolute entropy from temperature and pressure

If the can is left in a car that reaches 50 ☌ on a hot day, what is the new pressure in the can? (b) The gas in the can is initially at 24 ☌ and 360 kPa, and the can has a volume of 350 mL. (a) On the can is the warning “Store only at temperatures below 120 ☏ (48.8 ☌). Predicting Change in Pressure with TemperatureĪ can of hair spray is used until it is empty except for the propellant, isobutane gas. (Also note that there are at least three ways we can describe how the pressure of a gas changes as its temperature changes: We can use a table of values, a graph, or a mathematical equation.) Note that temperatures must be on the kelvin scale for any gas law calculations (0 on the kelvin scale and the lowest possible temperature is called absolute zero). This equation is useful for pressure-temperature calculations for a confined gas at constant volume. If the gas is initially in “Condition 1” (with P = P 1 and T = T 1), and then changes to “Condition 2” (with P = P 2 and T = T 2), we have that P 1 T 1 = k P 1 T 1 = k and P 2 T 2 = k, P 2 T 2 = k, which reduces to P 1 T 1 = P 2 T 2. Where ∝ means “is proportional to,” and k is a proportionality constant that depends on the identity, amount, and volume of the gas.įor a confined, constant volume of gas, the ratio P T P T is therefore constant (i.e., P T = k P T = k). P ∝ T or P = constant × T or P = k × T P ∝ T or P = constant × T or P = k × T We will consider the key developments in individual relationships (for pedagogical reasons not quite in historical order), then put them together in the ideal gas law. Eventually, these individual laws were combined into a single equation-the ideal gas law-that relates gas quantities for gases and is quite accurate for low pressures and moderate temperatures. Although their measurements were not precise by today’s standards, they were able to determine the mathematical relationships between pairs of these variables (e.g., pressure and temperature, pressure and volume) that hold for an ideal gas-a hypothetical construct that real gases approximate under certain conditions. Use the ideal gas law, and related gas laws, to compute the values of various gas properties under specified conditionsĭuring the seventeenth and especially eighteenth centuries, driven both by a desire to understand nature and a quest to make balloons in which they could fly ( Figure 9.9), a number of scientists established the relationships between the macroscopic physical properties of gases, that is, pressure, volume, temperature, and amount of gas.Identify the mathematical relationships between the various properties of gases.

By the end of this section, you will be able to:

Calculate absolute entropy from temperature and pressure