heat capacity

Examples of heat capacity in the following topics:

• Specific Heat and Heat Capacity

  • the molar heat capacity, which is the heat capacity per mole of a pure substance.
  • Molar heat capacity is often designated CP, to denote heat capacity under constant pressure conditions, as well as CV, to denote heat capacity under constant volume conditions.
  • Units of molar heat capacity are $\frac{J}{K\bullet mol}$.
  • the specific heat capacity, often simply called specific heat, which is the heat capacity per unit mass of a pure substance.
  • Now we can plug our values into the formula that relates heat and heat capacity:

• Constant-Pressure Calorimetry

  • Data collected during a constant-pressure calorimetry experiment can be used to calculate the heat capacity of an unknown substance.
  • We already know our equation relating heat (q), specific heat capacity (C), and the change in observed temperature ($\Delta T$) :
  • We will now illustrate how to use this equation to calculate the specific heat capacity of a substance.
  • The specific heat capacity of the unknown metal is 0.166 $\frac {J} {g ^\circ C}$ .
  • The number of joules of heat released into each gram of the solution is calculated from the product of the rise in temperature and the specific heat capacity of water (assuming that the solution is dilute enough so that its specific heat capacity is the same as that of pure water's).

• Constant-Volume Calorimetry

  • The total heat given off in the reaction will be equal to the heat gained by the water and the calorimeter:
  • Keep in mind that the heat gained by the calorimeter is the sum of the heat gained by the water, as well as the calorimeter itself.
  • where Cwater denotes the specific heat capacity of the water ($1 \frac{cal}{g ^{\circ}C}$), and Ccal is the heat capacity of the calorimeter (typically in $\frac{cal}{^{\circ}C}$).
  • The sample is ignited by an iron wire ignition coil that glows when heated.
  • From the change in temperature, the heat of reaction can be calculated.

• Heating Curve for Water

  • A heating curve shows how the temperature changes as a substance is heated up at a constant rate.
  • A constant rate of heating is assumed, so that one can also think of the x-axis as the amount of time that goes by as a substance is heated.
  • The amount of heat added, q, can be computed by: $q=m\cdot C_{H_2O(s)}\cdot \Delta T$ , where m is the mass of the sample of water, C is the specific heat capacity of solid water, or ice, and $\Delta T$ is the change in temperature during the process.
  • Note that the specific heat capacity of liquid water is different than that of ice.
  • Note that the specific heat capacity of gaseous water is different than that of ice or liquid water.

• Change in Enthalpy

  • By absorbing heat, the temperature, and thus the enthalpy of a substance increases.
  • The relationship is shown as: $\Delta H = C\rho \Delta T$, where $C\rho$ is the heat capacity of the material.
  • We discuss where the energy in chemical bonds comes from in terms of internal energy and enthalpy, as well as how to approximate the overall heat of reaction using bond enthalpies.

• Metallic Crystals

  • Electrical conductivity, as well as the electrons' contribution to the heat capacity and heat conductivity of metals, can be calculated from the free electron model, which does not take the detailed structure of the ion lattice into account.
  • Mechanical properties of metals include malleability and ductility, meaning the capacity for plastic deformation.
  • Applied heat, or forces larger than the elastic limit, may cause an irreversible deformation of the object, known as plastic deformation or plasticity.

• Free Energy and Work

  • As in mechanics, where potential energy is defined as capacity to do work, different potentials have different meanings.
  • Energy that is not extracted as work is exchanged with the surroundings as heat.
  • The appellation "free energy" for G has led to so much confusion that many scientists now refer to it simply as the "Gibbs energy. " The "free" part of the older name reflects the steam-engine origins of thermodynamics, with its interest in converting heat into work.

• New Energy Sources

  • Renewable energy is energy that comes from natural resources, such as sunlight, wind, rain, tides, waves, and geothermal heat, which are all naturally replenished.
  • At the end of 2011, the photovoltaic (PV) capacity worldwide was 67,000 MW.
  • In addition, solar thermal power stations, which are power plants that generate electricity from the heat of the sun's rays, operate in the USA and Spain.
  • The world's largest geothermal power installation is the Geysers complex in California, with a rated capacity of 750 MW.
  • Total renewable power capacity has been increasing over the past several years, from roughly 100 GW in 2005 to nearly 400 GW in 2007.

• Heat and Work

  • Heat transfer by convection occurs through a medium.
  • Lastly, heat can also be transferred by radiation; a hot object can convey heat to anything in its surroundings via electromagnetic radiation.
  • Like heat, the unit measurement for work is joules (J).
  • Heat and work are related.
  • Work can be completely converted into heat, but the reverse is not true: heat energy cannot be wholly transformed into work energy.

• Sulfur Compounds

  • Hydrogen sulfide gas and the hydrosulfide anion are extremely toxic to mammals, because they inhibit the oxygen-carrying capacity of hemoglobin and certain cytochromes in a manner similar to cyanide and azide.
  • Heating this compound gives polymeric sulfur nitride ((SN)x), which has metallic properties even though it does not contain any metal atoms.
  • In the most common type of industrial "curing" or hardening and strengthening of natural rubber, elemental sulfur is heated with the rubber until chemical reactions form disulfide bridges between isoprene units of the polymer.
  • Because of the heat and sulfur, the process was named vulcanization, after the Roman god of the forge and volcanism.