Chemistry_Grade_10-12 (1).pdf

146 chapter 8 thermal properties and ideal gases 2

Info icon This preview shows pages 160–163. Sign up to view the full content.

146
Image of page 160

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

CHAPTER 8. THERMAL PROPERTIES AND IDEAL GASES - GRADE 11 8.9 2. Forces of attraction do exist between molecules At low temperatures, when the speed of the molecules decreases and they move closer together, the intermolecular forces become more apparent. As the attraction between molecules increases, their movement decreases and there are fewer collisions between them. The pressure of the gas at low temperatures is therefore lower than what would have been expected for an ideal gas (figure 8.7. If the temperature is low enough or the pressure high enough, a real gas will liquify . ideal gas real gas Pressure Temperature Figure 8.7: Gases deviate from ideal gas behaviour at low temperatures 8.9 Summary The kinetic theory of matter helps to explain the behaviour of gases under different conditions. An ideal gas is one that obeys all the assumptions of the kinetic theory. A real gas behaves like an ideal gas, except at high pressures and low temperatures. Under these conditions, the forces between molecules become significant and the gas will liquify. Boyle’s law states that the pressure of a fixed quantity of gas is inversely proportional to its volume, as long as the temperature stays the same. In other words, pV = k or p 1 V 1 = p 2 V 2 . Charles’s law states that the volume of an enclosed sample of gas is directly proportional to its temperature, as long as the pressure stays the same. In other words, V 1 T 1 = V 2 T 2 The temperature of a fixed mass of gas is directly proportional to its pressure, if the volume is constant. In other words, p 1 T 1 = p 2 T 2 In the above equations, temperature must be written in Kelvin . Temperature in degrees Celsius (temperature = t) can be converted to temperature in Kelvin (temperature = T) using the following equation: T = t + 273 147
Image of page 161
8.9 CHAPTER 8. THERMAL PROPERTIES AND IDEAL GASES - GRADE 11 Combining Boyle’s law and the relationship between the temperature and pressure of a gas, gives the general gas equation , which applies as long as the amount of gas remains constant. The general gas equation is pV = kT, or p 1 V 1 T 1 = p 2 V 2 T 2 Because the mass of gas is not always constant, another equation is needed for these situations. The ideal gas equation can be written as pV = nRT where n is the number of moles of gas and R is the universal gas constant, which is 8.3 J.K 1 .mol 1 . In this equation, SI units must be used. Volume (m 3 ), pressure (Pa) and temperature (K). The volume of one mole of gas under STP is 22.4 dm 3 . This is called the molar gas volume . s Exercise: Summary exercise 1. For each of the following, say whether the statement is true or false . If the statement is false, rewrite the statement correctly. (a) Real gases behave like ideal gases, except at low pressures and low tem- peratures.
Image of page 162

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

Image of page 163
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern