16 Conservation of Heat Energy (First Law of Thermodynamics)
16 Conservation of Heat Energy (First Law of Thermodynamics)
Resources
- Video to Watch: Mechanical Universe – Episode 47 – Entropy
- Video to Watch: Mechanical Universe – Episode 48 – Low Temperatures
- Extra Help: A-Level Physics Tutor
Equations Introduced and Used in this Topic:
- [latex]\text{Heat}_{\text{Loss}}+ \text{Heat}_{\text{Gains}}= 0[/latex]
- [latex]Q_{\text{loss}} + Q_{\text{gain}}= 0[/latex]
- [latex]\Delta U=Q-W[/latex]
[latex]Q_i+E_{ki}+E_{pi}=E_{kf}+E_{pf}+Q_{f}[/latex] or [latex]\Delta Q+\Delta E_k+\Delta E_p=\text{ Constant}[/latex]
- [latex]Q=mc\Delta T[/latex]
- [latex]Q=\pm mL_f[/latex]
- [latex]Q=\pm mL_v[/latex]
- [latex]E_p=mgh[/latex]
- [latex]E_k=\dfrac{1}{2}mv^2[/latex]
- [latex]\text{Power }(P)=\dfrac{W}{t}=\dfrac{\Delta \text{Energy}}{t}[/latex]
- [latex]\text{Efficiency}=\dfrac{\text{Output}}{\text{Input}}\times100\%[/latex]
Where…
- [latex]∆U[/latex] is the Total Internal Energy of a System, measured in joules (J)
- [latex]Q[/latex] is the Heat (energy), measured in joules (J)
- [latex]L_v[/latex] is the Latent Heat of Vaporization, measured in joules/kilogram (J/kg)
- [latex]L_f[/latex] is the Latent Heat of Fusion, measured in joules/kilogram (J/kg)
- [latex]∆T[/latex] is the Change in Temperature (Tf – Ti), measured in Celsius (°C) or Kelvin (K)
- [latex]c[/latex] is the specific heat constant, measured in joules/kilogram degrees Celsius (J/kg°C). Specific heat is found by experiment but has a rough value for specific temperature ranges.
- [latex]E_p[/latex] is Potential Energy, measured in joules (J)
- [latex]E_k[/latex] is Kinetic Energy, measured in joules (J)
- [latex]m[/latex] is the Mass of the object, measured in kilograms (kg)
- [latex]g[/latex] or [latex]a_g[/latex] is the Gravitational Field Strength, measured in metres per second squared (m/s2)
- [latex]h[/latex] is the change in Vertical Height, measured in metres (m)
- [latex]v[/latex] is the Speed of the object, measured in metres per second (m/s)
- [latex]P[/latex] is the Power, measured in watts (W)
- [latex]W[/latex] is Work, measured in joules (J)
- [latex]t[/latex] is Time, measured in seconds (s)
- [latex]∆\text{Energy}[/latex] is the change in a combination of Mechanical and Heat Energy forms
([latex]\Delta E_p = E_{pf}- E_{pi}[/latex], [latex]\Delta E_k=E_{kf}-E_{ki}[/latex] or [latex]\Delta Q=Q_f-Q_i[/latex]) and is measured in joules (J).
| Material | Specific Heat | Material | Specific Heat |
|---|---|---|---|
| Aluminum | 900 J/kg°C | Lead | 160 J/kg°C |
| Brass | 384 J/kg°C | Mercury | 139 J/kg°C |
| Copper | 390 J/kg°C | Pyrex | 837 J/kg°C |
| Ethanol | 2400 J/kg°C | Silver | 235 J/kg°C |
| Glass | 840 J/kg°C | Steel | 445 J/kg°C |
| Ice | 2100 J/kg°C | Steam | 2020 J/kg°C |
| Iron | 460 J/kg°C | Water | 4187 J/kg°C |
| Material | Lf (J/kg) | Lv (J/kg) |
|---|---|---|
| Water | 3.34 × 105 | 2.26 × 106 |
| Mercury | 1.18 × 104 | 2.96 × 105 |
| Ethyl Alcohol | 1.05 × 105 | 8.54× 105 |
| Nitrogen | 2.55 × 104 | 1.99 × 105 |
| Oxygen |