Thermal Expansion of Materials

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Questions and Answers

What is thermal expansion?

  • A decrease in the size of an object with a decrease in its temperature
  • An increase in the size of an object with an increase in its temperature (correct)
  • A change in the density of an object with a change in its volume
  • A change in the shape of an object with a change in its pressure

What happens to the average separation between the atoms in an object when it undergoes thermal expansion?

  • It becomes zero
  • It remains the same
  • It decreases
  • It increases (correct)

What is similar to the notion of thermal expansion?

  • A geometric transformation of an object
  • A topological deformation of an object
  • A photographic reduction of an object
  • A photographic enlargement of an object (correct)

What happens to the hole of a metal washer when it is heated?

<p>It increases in size (A)</p> Signup and view all the answers

What is one of the intended learning objectives of this lesson?

<p>To define what is meant by the thermometric property (A)</p> Signup and view all the answers

What is the ideal gas law used for?

<p>To determine various properties of a gas (A)</p> Signup and view all the answers

What is the consequence of the change in the average separation between the atoms in an object?

<p>Thermal expansion (B)</p> Signup and view all the answers

What is linear expansion an example of?

<p>Thermal expansion (C)</p> Signup and view all the answers

What happens to the volume of most liquids, including acetone, when their temperature increases?

<p>They increase in volume (D)</p> Signup and view all the answers

What is the unusual behavior of water near 0°C?

<p>It contracts with increasing temperature (A)</p> Signup and view all the answers

What is the maximum density of water?

<p>1.000 g/cm³ (A)</p> Signup and view all the answers

What is assumed to be nonexistent in ideal gases?

<p>Interatomic forces (B)</p> Signup and view all the answers

What is the advantage of using the ideal gas model?

<p>It is simple to use (B)</p> Signup and view all the answers

What is the unit of Avogadro's number?

<p>no unit (it is a pure number) (C)</p> Signup and view all the answers

What is the molar mass of helium (He)?

<p>4.00 g/mol (C)</p> Signup and view all the answers

What is the relation between pressure and volume of an ideal gas at constant temperature?

<p>Pressure is inversely proportional to volume (D)</p> Signup and view all the answers

What is the name of the equation that interrelates the variables of an ideal gas?

<p>Gas Equation of State (A)</p> Signup and view all the answers

What is the purpose of the movable piston in the ideal gas experiment?

<p>To vary the volume of the gas (B)</p> Signup and view all the answers

What happens to the radius of a hole in a piece of material when it expands thermally?

<p>The radius of the hole increases (C)</p> Signup and view all the answers

What is the relationship between the change in dimension and the change in temperature for small expansions?

<p>The change in dimension is proportional to the first power of the change in temperature (A)</p> Signup and view all the answers

What is the unit of the coefficient of linear expansion?

<p>(ºC)–1 (C)</p> Signup and view all the answers

What is the formula for the change in length of an object due to thermal expansion?

<p>ΔL = αLiΔT (C)</p> Signup and view all the answers

What is the assumption made in the formula for linear expansion?

<p>The expansion is sufficiently small (B)</p> Signup and view all the answers

What happens to the bolts in the poorly designed electronic device when it expands thermally?

<p>They move farther apart (B)</p> Signup and view all the answers

What is the formula for the final length of an object after thermal expansion?

<p>Lf = Li + αLiΔT (B)</p> Signup and view all the answers

What is the definition of the coefficient of linear expansion?

<p>α = ΔL/LiΔT (D)</p> Signup and view all the answers

What is the primary purpose of the compression process in an automobile engine?

<p>To prepare the air-gasoline mixture for ignition (D)</p> Signup and view all the answers

What is the compression ratio of a typical automobile engine?

<p>9.00 to 1 (A)</p> Signup and view all the answers

What is the purpose of the intake and exhaust valves in an automobile engine?

<p>To remain closed during the compression process (B)</p> Signup and view all the answers

What is the result of compressing the gas in the cylinders of an automobile engine?

<p>The temperature of the gas increases (C)</p> Signup and view all the answers

What is the initial pressure of the gas in the SAMPLE PROBLEM 4?

<p>1.00 atm (B)</p> Signup and view all the answers

What is the final pressure of the gas in the SAMPLE PROBLEM 4?

<p>21.70 atm (A)</p> Signup and view all the answers

What is the initial temperature of the gas in the SAMPLE PROBLEM 4?

<p>27.0°C (A)</p> Signup and view all the answers

What happens to the volume of the gas in the cylinders during the compression process?

<p>It decreases to 1/9.00 of its original volume (C)</p> Signup and view all the answers

What is the relationship between the pressure of a gas and its temperature when the volume of the gas is kept constant?

<p>The pressure of the gas is directly proportional to its temperature. (C)</p> Signup and view all the answers

What is the equation that combines and summarizes the other gas laws?

<p>PV = nRT (D)</p> Signup and view all the answers

What is the value of the Universal Gas Constant R?

<p>8.314 J/mol ∙ K = 0.08214 L ∙ atm/mol ∙ K (D)</p> Signup and view all the answers

What is the value of Boltzmann's constant k_B?

<p>1.38 × 10^(-23) J/K (B)</p> Signup and view all the answers

What is the ideal gas law often expressed in terms of?

<p>The total number of molecules, N, present in the sample (C)</p> Signup and view all the answers

What is the relationship between the volume of a gas and its temperature when the pressure of the gas is kept constant?

<p>The volume of the gas is directly proportional to its temperature. (C)</p> Signup and view all the answers

What is the significance of the value 22.4 L?

<p>It is the volume of 1 mole of any gas at atmospheric pressure and at 0°C. (C)</p> Signup and view all the answers

What are the thermodynamic variables of an ideal gas?

<p>P, V, and T (D)</p> Signup and view all the answers

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Study Notes

Thermal Expansion

  • Thermal expansion is the increase in size of an object with an increase in its temperature.
  • This is a consequence of the change in the average separation between the atoms in an object.
  • The notion of thermal expansion can be thought of as being similar to a photographic enlargement of an object.
  • As an object is heated, all its dimensions will increase, including the size of a hole in the object.

Linear Expansion

  • Linear expansion is the increase in length of an object with an increase in temperature.
  • The coefficient of linear expansion, α, is defined as the change in length (ΔL) per unit original length (Li) per unit change in temperature (ΔT).
  • α has units of (ºC)–1.
  • The change in length (ΔL) can be calculated using the formula: ΔL = αLiΔT.

Area and Volume Expansion

  • Area and volume expansion occur when the surface area and volume of an object increase with an increase in temperature.
  • The expansion of a cavity in a piece of material occurs in the same way as if the cavity were filled with the material.

Ideal Gas

  • An ideal gas is a hypothetical gas that obeys the ideal gas law: PV = nRT.
  • The ideal gas law combines and summarizes the other gas laws, such as Boyle's Law, Charles' Law, and Gay-Lussac's Law.
  • R is the universal gas constant, with a value of 8.314 J/mol·K.
  • One mole of any gas at atmospheric pressure and at 0ºC is 22.4 L.

Macroscopic Description of an Ideal Gas

  • The equation of state for an ideal gas is PV = nRT.
  • The ideal gas model can be used to make predictions that are adequate to describe the behavior of real gases at low pressures.
  • The amount of gas in a given volume is conveniently expressed in terms of the number of moles, n.
  • Avogadro's number (NA) is 6.022 x 10²³.

Thermometric Property

  • The thermometric property is a measure of the thermal expansion of an object.
  • The coefficient of linear expansion (α) is used to calculate the change in length of an object due to a change in temperature.

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