PX154 - B3 - heat capacity

[YF 17.4]

• we can have heat flow, $Q$ into or out of a system which will increase or decrease its temperature
  • if $Q$ is:
    • positive : heat in
    • negative : heat out
  • heat in/out increases/decreases the system's internal energy
• here, we define molar and specific heat capacities
  • molar ($C$):
  $$\mathrm{\Delta }T=\frac{Q}{nC}$$where $n\equiv$ number of moles
  • specific($c/C_m$):
  $$\mathrm{\Delta }T=\frac{Q}{mc}=\frac{Q}{m{C}_m}$$where $m=$ mass in kg
  • eg: $c_{water}=4190Jk{g}^{-1}{K}^{-1}$

latent heat

• heat exchange during a phase transition
  • units: $J.k{g}^{-1}$
  • heat flow $Q=\pm mL$
    $+\to$ heat in
    $-\to$ heat out
    $m=$ mass
    $L=$ latent heat
  • types:
    • solid $\leftrightarrow$ liquid : latent heat of fusion
    • liquid $\leftrightarrow$ gas: latent heat of vaporization
  • [YF table 17.4]
    • 
  • water:
    • $L_f=3.34\times {10}^{5}Jk{g}^{-1}$
    • $L_v=2.26\times {10}^{6}Jk{g}^{-1}$