Relationships among Pressure, Temperature, Volume, and Amount - Chemistry LibreTexts
The Gas Laws: Pressure Volume Temperature Relationships Where n is the number of moles of the number of moles and R is a constant called the universal . How many moles of gas occupy 98 L at a pressure of 2. ; Naming In chemistry, the relationships between gas physical properties are described as gas laws. .. Section A community chest, corporation, trust, fund, or foundation organized or. pressure, V is the volume of the gas, n is the number of moles . fluids, the shear stress is directly proportional to the velocity gradient.
Pressure is force per unit area, calculated by dividing the force by the area on which the force acts. The earth's gravity acts on air molecules to create a force, that of the air pushing on the earth. This is called atmospheric pressure. The units of pressure that are used are pascal Pastandard atmosphere atmand torr.
It is normally used as a standard unit of pressure. The SI unit though, is the pascal. For laboratory work the atmosphere is very large.
Calorimetry and enthalpy introduction (video) | Khan Academy
A more convient unit is the torr. A torr is the same unit as the mmHg millimeter of mercury. It is the pressure that is needed to raise a tube of mercury 1 millimeter.
The Pressure-Volume Law Boyle's law or the pressure-volume law states that the volume of a given amount of gas held at constant temperature varies inversely with the applied pressure when the temperature and mass are constant.
Another way to describing it is saying that their products are constant. When volume goes up, pressure goes down. Let's examine the parts of this. First of all, the heat change in the calorimeter is normally represented by a lowercase "q," but it can also be represented by change in enthalpy, or delta H, because remember that constant pressure delta H equals q, and constant pressure is almost always a good assumption for the duration of an experiment, or at least as long as we stay at the surface of the earth.
For reasons that will become clear later, we'll sure delta H to represent the heat change for this experiment. Specific heat capacity, represented by a lowercase "s", is the amount of heat required tp raise the temperature of one mass unit, like a gram or kilogram, of a substance by 1 degree Celsius.
So it turns out that different amounts of heat create different temperature changes, like metals get hot really easily and cool down really easily. Others like water require a lot of thermal energy to raise the temperature, and therefore have to release a lot of heat to cool down. I'm always wondering though, like, what does that really mean? Like, physically in the molecules, shouldn't heat raise the temperature of all substances equally?
Earths atmosphere before the age of dinosaurs
And why does water in particular have such a high specific heat capacity? Heat energy can do a lot of things besides just increase temperatures. Temperature, or the speed at which molecules bounce around, is just one way that atoms or molecules can absorb energy. Heat energy can also be absorbed by the breaking and formation of bonds between molecules, and as we'll learn in another episode, the extremely high specific heat capacity of water is due to the breaking and formation of hydrogen bonds that are associated with relatively small changes in temperature.
And how do we know the specific heat capacity? Well, I am happy to report that some noble chemists have worked hard to determine the specific heat capacities of hundreds of substances so that we don't have to. We just have to look up the numbers in a table. Okay, so specific heat capacity times mass times the change in temperature.
The mass is important because the more mass of a substance we have, the more chemical bonds are present, and because energy is contained in chemical bonds, they have a big effect on how much energy we're able to absorb or release. And finally, there's the change in temperature. When doing calorimetry, we calculate a change in heat by measuring a change in temperature, but as we've said a billion times before, heat and temperature are not the same thing.
But please do not think that this thing is measuring heat because it's not! It's just that luckily, in this specific case, they are related by our handy little calorimeter formula.
Now you might not have noticed, but we are right at the interface between chemistry and physics here. Each science could claim ownership over this phenomenon, but the truth is humans made up the difference between chemistry and physics anyway. Thermodynamics, the study of heat, energy, and work, doesn't care about our little rules.
Thermodynamics itself makes the rules of the universe. It is the ultimate law. So now you know, even though you might not have cared, but you should! It's all wiggly-wobbly bondy-wondy. Enough talk, let's get out there, actually do some math here.
Remember that the formula is delta H, s, m, delta T. The solutions we're using here are so dilute that almost all of their mass consists of water. Therefore, we can use the specific heat capacity of water. If we look that up on our table, we'll see that it is 4. And finally, we need the temperature change. If you remember, the temperature rose from It's a positive value because the temperature increased.
Cancel out all the appropriate units and then bang on the calculator to get a final release of This led to the giant flying creatures close to the end of the dinosaur age.
It could be that these creatures died out as the total pressure of the atmosphere dropped below their sustainable level Figure 7. Limestone caves There are many limestone caves throughout the world, some of which are several kilometers long.
This tells us something about our atmosphere as well. Because of its high concentration in the atmosphere, CO2 dissolved in rainwater and groundwater, and the reaction was driven to the right. When the atmosphere becomes lean in CO2, the reaction shifts to the left.
The fact that the limestone caves were formed relatively recently indicates that the CO2 concentration in the atmosphere was very high long ago, leading to the deposits of limestone, but became very low recently, allowing limestone to dissolve. In high-CO2 atmospheres and other hostile environments, life forms can take advantage of free energy in an amazing range of environments: On a more familiar level, the microbe that produces champagne bubbles operates at pressures up to 7 bar of CO2.
Other estimates of CO2 concentrations Researchers have speculated that the CO2 concentration may have been somewhat higher in the past than it is today.
Studying carbon exchange between mantle and crust, Des Marais suggests that Mya, the atmosphere contained at least times as much CO2 or 0. Many other such proposals have been put forth. Plant growth at high CO2 concentrations It is pertinent to ask whether any experiments have been performed to suggest whether life could thrive at higher CO2 concentrations. We put this proposal to the test by growing plants in 32 sealed containers 1- and 2-L plastic soda bottles containing weighed amounts of CO2 at pressures from 2 to 10 bar.
In general, however, plant growth was considerably slower than at 1 bar. Mosses, ferns, and flowering plants died within a month at these high CO2 levels. The poor growth observed in these experiments is most likely due to the buildup of product gases in the sealed containers, rather than high CO2 pressure, and therefore these results could be flawed.
We would expect that vigorous growth would be observed in a continually rejuvenated atmosphere. How did the flying creatures from the age of dinosaurs have enough energy to fly when physiology, biology, and aeronautics say that this was impossible? How could life have developed on Earth when astronomy says that Earth was too cold to sustain life? This picture of high CO2 concentration and high pressure in the past also explains why most massive coal seams are older than 65 million years and why most limestone caves are younger than million years.
Although we do not know the values for the atmospheric pressure in those early times, and although each of the arguments in this paper only leads to suggestions, when taken together, the evidence from these various sources leads to the same conclusion: The atmospheric pressure was higher in the past than it is today and consisted primarily of CO2.
This hypothesis presents a picture of our evolving planet that should be examined and that could have interesting consequences.
Map; National Geographic, April Origin of Continents and Oceans; Biram, J. Continents in Motion; McGraw-Hill: Cleveland, ; p F In Geophysical Monograph Series, Vol. Chemical Process Principles, Part 1, 2nd ed. New York, ; p New York, ; Vol.