heat of solution

(noun)

The enthalpy change associated with the dissolution of a substance in a solvent at constant pressure, resulting in infinite dilution.

Related Terms

Examples of heat of solution in the following topics:

  • Heat of Solution

    • Heat of solution refers to the change in enthalpy when a solute is dissolved into a solvent.
    • The heat of solution, also referred to the enthalpy of solution or enthalpy of dissolution, is the enthalpy change associated with the dissolution of a solute in a solvent at constant pressure, resulting in infinite dilution.
    • The heat of solution, like all enthalpy changes, is expressed in kJ/mol for a reaction taking place at standard conditions (298.15 K and 1 bar).
    • The heat of solution can be regarded as the sum of the enthalpy changes of three intermediate steps:
    • The value of the overall heat of solution, $\Delta H^\circ_{sol}$, is the sum of these individual steps.

  • Solutions and Heats of Hydration

    • When ions dissolve in water, the stabilizing interactions that result release energy called the "heat of hydration."
    • M^+ (g) + X^-(g) \to M^+ (aq) + X^-(aq)$ [heat of hydration]
    • The heat (enthalpy) of solution (Hsolution) is the sum of the lattice and hydration energies ( Hsolution = Hhydration + Hlattice energy).
    • In case you were wondering where we got the term "heat of hydration," it has to do with the fact that some solutions are highly exothermic when formed.
    • A hot solution results when the heat of hydration is much greater than the lattice energy of the solute.

  • Constant-Pressure Calorimetry

    • The heat transferred to/from the solution in order for the reaction to occur is equal to the change in enthalpy ($\Delta H = q_P$), and a constant-pressure calorimeter thus measures this heat of reaction.
    • To determine the standard enthalpy of the reaction H+(aq) + OH–(aq) → H2O(l), equal volumes of 0.1 M solutions of HCl and of NaOH can be combined initially at 25°C.
    • This process is exothermic and as a result, a certain amount of heat qP will be released into the solution.
    • 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).
    • The total quantity of transferred heat can then be calculated by multiplying the result with the mass of the solution.

  • Solving Problems with Calorimetry

    • The change in temperature of the measuring part of the calorimeter is converted into the amount of heat (since the previous calibration was used to establish its heat capacity).
    • For example, when an exothermic reaction occurs in solution in a calorimeter, the heat produced by the reaction is absorbed by the solution, which increases its temperature.
    • When an endothermic reaction occurs, the heat required is absorbed from the thermal energy of the solution, which decreases its temperature.
    • 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.
    • Assuming perfect heat transfer, the heat given off by metal is the negative of the heat taken in by water, or:

  • Calorimetry

    • Calorimetry is the measurement of the heat of chemical reactions or physical changes.
    • Calorimetry is the science of measuring the heat of chemical reactions or physical changes.
    • A constant-pressure calorimeter measures the change in enthalpy of a reaction occurring in solution during which the atmospheric pressure remains constant.
    • The inner cup holds a known amount of a solute, usually water, that absorbs the heat from the reaction.
    • 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 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.
    • Instead, use the heat of fusion ($\Delta H_{fusion}$ ) to calculate how much heat was involved in that process: $q=m\cdot \Delta H_{fusion}$, where m is the mass of the sample of water.
    • Note that the specific heat capacity of liquid water is different than that of ice.
    • The liquid will begin to boil when enough heat has been absorbed by the solution that the temperature reaches the boiling point, where again, the temperature remains constant until all of the liquid has become gaseous water.
    • Use the heat of vaporization ($\Delta H_{vap}$ ) to calculate how much heat was absorbed in this process: $q=m\cdot C_{H_2O(g)}\cdot \Delta T$, where m is the mass of the sample of water.

  • Solubility

    • Solubility is the relative ability of a solute (solid, liquid, or gas) to dissolve into a solvent and form a solution.
    • The solubility of a substance in a particular solvent is measured by the concentration of the saturated solution.
    • A solution is considered saturated when adding additional solute no longer increases the concentration of the solution.
    • As water molecules heat up, they vibrate more quickly and are better able to interact with and break apart the solute.
    • Pressure has a negligible effect on the solubility of solid and liquid solutes, but it has a strong effect on solutions with gaseous solutes.

  • Convection

    • Example: Calculating Heat Transfer by Convection: Convection of Air Through the Walls of a House.
    • Strategy Heat is used to raise the temperature of air so that Q=mcΔT.
    • The rate of heat transfer is then Q/t, where t is the time for air turnover.
    • The specific heat of air is a weighted average of the specific heats of nitrogen and oxygen, which is c=cp≅1000 J/kg⋅C (note that the specific heat at constant pressure must be used for this process).
    • Solution (1) Determine the mass of air from its density and the given volume of the house.

  • Specific Heat

    • However, it would be pretty inconvenient to measure the heat capacity of every unit of matter.
    • The specific heat is the amount of heat necessary to change the temperature of 1.00 kg of mass by 1.00ºC.
    • Note that the total heat capacity C is simply the product of the specific heat capacity c and the mass of the substance m, i.e.,
    • The specific heat of water is five times that of glass and ten times that of iron, which means that it takes five times as much heat to raise the temperature of water the same amount as for glass and ten times as much heat to raise the temperature of water as for iron.
    • Listed are the specific heats of various substances.

  • Water’s High Heat Capacity

    • The high heat capacity of water has many uses.
    • The heat is quickly transferred to a pool of water to cool the reactor.
    • 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.