specific heat

Examples of specific heat in the following topics:

• Specific Heat

  • This quantity is known as the specific heat capacity (or simply, the specific heat), which is the heat capacity per unit mass of a material .
  • The last two factors are encapsulated in the value of the specific heat.
  • The specific heat is the amount of heat necessary to change the temperature of 1.00 kg of mass by 1.00ºC.
  • In general, the specific heat also depends on the temperature.
  • Listed are the specific heats of various substances.

• Specific Heat and Heat Capacity

  • the specific heat capacity, often simply called specific heat, which is the heat capacity per unit mass of a pure substance.
  • Given the molar heat capacity or the specific heat for a pure substance, it is possible to calculate the amount of heat required to raise/lower that substance's temperature by a given amount.
  • In these equations, m is the substance's mass in grams (used when calculating with specific heat), and n is the number of moles of substance (used when calculating with molar heat capacity).
  • Specific heat capacity is the measure of the heat energy required to raise the temperature of a given quantity of a substance by one kelvin.
  • The above simulation demonstrates the specific heat and the latent heat.

• Water’s High Heat Capacity

  • The high heat capacity of water has many uses.
  • The capability for a molecule to absorb heat energy is called heat capacity, which can be calculated by the equation shown in the figure .
  • Water has the highest specific heat capacity of any liquid.
  • Specific heat is defined as the amount of heat one gram of a substance must absorb or lose to change its temperature by one degree Celsius.
  • In fact, the specific heat capacity of water is about five times more than that of sand.

• Constant-Pressure Calorimetry

  • 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.
  • What is the specific heat of the unknown metal?
  • (The specific heat of water is 4.18 $\frac {J} {g^\circ C}$)
  • The specific heat capacity of the unknown metal is 0.166 $\frac {J} {g ^\circ C}$ .

• Solving Problems with Calorimetry

  • To do so, the heat is exchanged with a calibrated object (calorimeter).
  • The temperature change, along with the specific heat and mass of the solution, can then be used to calculate the amount of heat involved in either case.
  • Use these data to determine the specific heat of the metal.
  • Assuming perfect heat transfer, the heat given off by metal is the negative of the heat taken in by water, or:
  • Our experimental specific heat is closest to the value for copper (0.39 J/g °C), so we identify the metal as copper.

• Calorimetry

  • Calorimetry requires that the material being heated have known thermal properties, i.e. specific heat capacities .
  • where δQ is the increment of heat gained by the sample, CV is the heat capacity at constant volume, cv is the specific heat at constant volume, and ΔT is the change in temperature.
  • Multiplying the temperature change by the mass and specific heat capacities of the substances gives a value for the energy given off or absorbed during the reaction:
  • It does not account for the heat loss through the container or the heat capacity of the thermometer and container itself.
  • where Cp is the specific heat at constant pressure, ΔH is the enthalpy of the solution, ΔT is the change in temperature, W is the mass of the solute, and M is the molecular mass of the solute.

• 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.

• 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.

• Latent Heat

  • Previously, we have discussed temperature change due to heat transfer.
  • where the latent heat of fusion, Lf, and latent heat of vaporization, Lv, are material constants that are determined experimentally.
  • Lf and Lv are collectively called latent heat coefficients.
  • Once all the ice has melted, the temperature of the liquid water rises, absorbing heat at a new constant rate of 1.00 cal/g⋅C (remember that specific heats are dependent on phase).
  • Heat from the air transfers to the ice causing it to melt.

• Heat as Energy Transfer

  • Heat is the spontaneous transfer of energy due to a temperature difference.
  • This observation leads to the following definition of heat: Heat is the spontaneous transfer of energy due to a temperature difference .
  • Heat is often confused with temperature.
  • Heat is a form of energy, whereas temperature is not.
  • The calorie (cal) is a common unit of energy, defined as the energy needed to change the temperature of 1.00 g of water by 1.00ºC —specifically, between 14.5ºC and 15.5ºC, since there is a slight temperature dependence.