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By @timmossholder

Thermal Expansion of Materials

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Questions and Answers

What is thermal expansion?

An increase in the size of an object with an increase in its temperature

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

It increases

What is similar to the notion of thermal expansion?

A photographic enlargement of an object

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

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

What is the ideal gas law used for?

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

What is linear expansion an example of?

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

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

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

What is the maximum density of water?

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

What is assumed to be nonexistent in ideal gases?

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

What is the advantage of using the ideal gas model?

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

What is the unit of Avogadro's number?

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

What is the molar mass of helium (He)?

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

What is the unit of the coefficient of linear expansion?

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

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

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

What is the definition of the coefficient of linear expansion?

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

What is the compression ratio of a typical automobile engine?

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

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

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

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

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

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

<p>27.0°C</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</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.</p> Signup and view all the answers

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

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

What is the value of Boltzmann's constant k_B?

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

What are the thermodynamic variables of an ideal gas?

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

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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