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Chapter 14 The Gas Laws

Chapter 14 The Gas Laws. Pages 418 - 443. The Kinetic molecular theory that we talked about in the last is still valid. Gases are in constant random motion. Collisions between gas particles are elastic. Gases are considered to be point masses.

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Chapter 14 The Gas Laws

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  1. Chapter 14The Gas Laws Pages 418 - 443

  2. The Kinetic molecular theory that we talked about in the last is still valid. • Gases are in constant random motion. • Collisions between gas particles are elastic. • Gases are considered to be point masses. • The speed of gas particles is directly related to the temperature of the gas. • Actual gases don’t obey all parts of the Kinetic Theory. • Directly related means that it changes the same way. • Inversely related means that it changes in an opposite manner.

  3. Boyle’s Law • At a constant temperature, the pressure of a gas and the volume of a gas vary inversely. • Boyle discovered that the pressure of a gas times its volume was always equal to a constant value at a constant temperature. • P1V1 = P2V2

  4. Charles ‘s Law • At a constant pressure, the volume of a gas and its temperature vary directly. • Charles discovers that volume divided by temperature is a constant value at a constant pressure. • To eliminate zero and negative numbers, temperatures must be in Kelvins. ( oC + 273 = K ) • V1 / T1 = V2 / T2

  5. Gay – Lussac’s Law • At a constant volume, pressure and temperature vary directly. • P1 / T1 = P2 / T2 • Avogadro’s Principle • At constant temperature and pressure the volume and number of particles of a gas vary directly. • V1 / n1 = V2 / n2( n = moles)

  6. The Combined Gas Law • We can put these laws together to create one equation. • P1 V1 / n1 T1 = P2 V2 / n2 T2 • This one law can be used in place of any of the other laws. • If a quantity is not give or is said to be constant, it can be dropped out of the equation.

  7. Ideal Gas Law • We can further simplify the equation if we choose one set of conditions to always be Standard Temperature and Pressure. • We can then replace the right side of the equation with R, the ideal gas constant. By rearranging the equation we get the ideal gas equation. • P V = n R T • Where R = 0.0821 L atm / mol K = 8.31 L kPa / mol K = 62.4 L mmHg / mol K

  8. Variations of the Ideal Gas Law • By either rearranging the equation or substituting in other equations, we can change the equation. • Molar Mass of a gas P V = m R T / M Where m is the mass of the gas and M is its molar mass. • Density of a Gas D = (m/V) = M P / R T

  9. Real Gases • As stated previously, real gases do not follow the Kinetic molecular theory exactly. Because of this Real gases do not behave exactly like ideal gases. • The key points that differ are that real gases do have some small volume and that there are some attractive forces between gas particles. • Under most normal conditions, real gases behave very closely to ideal gases, but under low temperatures and high pressures these differences become large enough to cause variations in behavior.

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