Terms

Terms

TermDefinition
Heat capacitythe amount of heat required to raise the temperature of a substance by 1 K or 1°C
Specific Heat capacityis the amount of heat required to raise the temperature of a unit mass of a substance by 1 K or 1°C
Latent heatthe energy released or absorbed by a substance during a change of state, without a change in its temperature
Specific latent heat of fusionthe amount of heat required to change a unit mass of a substance from solid state to liquid state, without a change in temperature
Specific latent heat of vaporisationthe amount of heat required to change a unit mass of a substance from liquid state to gaseous state, without a change in temperature

info

  • Latent heat of vaporisation and fusion
    • For the same mass of substances, more energy is released when it changes from gaseous state to the liquid state than when it changes from the liquid state to the solid state
    • This is because the average difference in intermolecular distance between molecules in gaseous state compared to the liquid state is very large, whereas the difference in intermolecular distance between the liquid and solid states is relatively small
    • As a result, for most substances, the specific latent heat of vaporisation is greater than the specific latent heat of fusion
  • Newton's law of cooling
    • The rate of cooling is directly proportional to the temperature differnce

Formulae

C=m×cwhereCheat capacity in J K−1mmass in kgcspecific heat capacity in J Kg−1 K−1\begin{array}{c} \begin{aligned} C &= m \times c \end{aligned} \\ \hspace{-9em}\textbf{where} \\ \begin{array}{rl} C & \text{heat capacity in $J\ K^{-1}$} \\ m & \text{mass in kg} \\ c & \text{specific heat capacity in $J\ Kg^{-1}\ K^{-1}$} \end{array} \end{array} C=QΔΘwhereCheat capacity in J K−1Qenergy transfered by heating in JΔΘchange in temperature in K\begin{array}{c} \begin{aligned} C &= \frac{Q}{\Delta \Theta} \end{aligned} \\ \hspace{-9em}\textbf{where} \\ \begin{array}{rl} C & \text{heat capacity in $J\ K^{-1}$} \\ Q & \text{energy transfered by heating in $J$} \\ \Delta \Theta & \text{change in temperature in $K$} \end{array} \end{array} c=QmΔΘwherecspecific heat capacity in J Kg−1 K−1Qenergy transferred by heating in Jmmass in KgΔΘchange in temperature in K\begin{array}{c} \begin{aligned} c &= \frac{Q}{m\Delta \Theta} \end{aligned} \\ \hspace{-9em}\textbf{where} \\ \begin{array}{rl} c & \text{specific heat capacity in $J\ Kg^{-1}\ K^{-1}$} \\ Q & \text{energy transferred by heating in $J$} \\ m & \text{mass in $Kg$} \\ \Delta \Theta & \text{change in temperature in $K$} \end{array} \end{array}

during state change,

Lf=Lv=QwhereLflatent heat of fusion in JLvlatent heat of vaporisation in JQenergy transfer in J\begin{array}{c} \begin{aligned} L_f &= L_v \\ &= Q \end{aligned} \\ \hspace{-9em}\textbf{where} \\ \begin{array}{rl} L_f & \text{latent heat of fusion in $J$} \\ L_v & \text{latent heat of vaporisation in $J$} \\ Q & \text{energy transfer in $J$} \end{array} \end{array} lf=lv=Qmwherelfspecific latent heat of fusion in J kg−1lvspecific latent heat of vaporisation in J kg−1Qenergy transferred in Jmmass in kg\begin{array}{c} \begin{aligned} l_f &= l_v \\ &= \frac{Q}{m} \end{aligned} \\ \hspace{-9em}\textbf{where} \\ \begin{array}{rl} l_f & \text{specific latent heat of fusion in $J\ kg^{-1}$} \\ l_v & \text{specific latent heat of vaporisation in $J\ kg^{-1}$} \\ Q & \text{energy transferred in $J$} \\ m & \text{mass in $kg$} \end{array} \end{array}
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