Chapter 3: Heat PDF

# Chapter 3: Heat ## Heat and Internal Energy - Heat is the transfer of energy between a system and its environment due to temperature differences. - Internal energy is the energy associated with the atoms and molecules of the system. - **Specific Heat**: the amount of energy needed to raise the...

# Chapter 3: Heat ## Heat and Internal Energy - Heat is the transfer of energy between a system and its environment due to temperature differences. - Internal energy is the energy associated with the atoms and molecules of the system. - **Specific Heat**: the amount of energy needed to raise the temperature of one kilogram of an arbitrary substance by 1°C. Varies with the substance. - Formula: $C = \frac{Q}{M \Delta T} = 1 \frac{kJ}{kg \cdot C°}$ - SI Unit: Joule/kilogram/ degree Celsius - Energy: $Q = C \cdot M \Delta T$ - **Heat Capacity**: the quantity of heat needed to increase the temperature by one degree 1°C. - Formula: $C = \frac{\Delta Q}{\Delta T}$ ## Calorimetry - $Q_\text{Cold}$ = $Q_\text{hot}$ - **Latent Heat & Phase Change** - $Q$ = the quantity of heat needed to change the phase of a given state - Formula: $Q = \pm m L$ - **Latent Heat**: The quantity of heat taken into or released without a change of temperature. Depends on the nature of the phase change. - **Latent Heat of Fusion** ($L_f$) - is used when a change in phase occurs during melting or freezing. - **Change of Phase**: The transformation from one state to another with no change in temperature. - Specific heat (water) = 4190 J/kg·K - Latent heat of fusion (water) = 3.33x10⁵ J/kg - Formula: $Q = m \cdot c \cdot \Delta T$ ± $mL$ ## Convection - **Convection**: the transfer of heat due to the movement of fluids (liquids - gasses - solids). - Ex: hot air - atmosphere - oceans - Formula: $Q = h \cdot A \cdot \Delta T$ - h = coefficient of convection - $A$ = depends on fluid geometry ## Radiation - **Radiation**: transfer of energy due to electromagnetic waves when thermal energy is converted by the movement of the charges of electrons and protons in materials. - Radiation doesn't need a temperature gradient - Radiation absorbed energy → electromagnetic waves. - Kinetic energy - rapidly moving atoms → electron magnetic waves → radiation energy ## Infrared Radiation - Travels in space with the same velocity of light, reflects, refracts according to the same laws of light, and is collected by concave mirrors or concave lenses. ## Thermal Expansion - **Thermal Expansion:** volume increases as temperature increases at constant pressure. - **Linear** (1-dimensional) / **Volumetric** (3-dimensional) - **Material's Coefficient of Expansion**: the amount a material expands. - **Expansion of Solids**: size ↑ T @ P. - Formula: $\alpha = \frac{\Delta L}{L_o \Delta T}$ - Unit: C^-1 ## Heat Transfer - **Heat Transfer**: transfers from high temperature regions to low temperature. - **Ends** when both regions are the same temperature. - **Condition**: difference in temperature. - **Conduction**: - Formula: $H = \frac{\Delta Q}{\Delta T} = \frac{K A (\theta_1 - \theta_2)}{L}$ - $K$ = constant (of the coefficient of thermal conductivity or conductivity) - Unit: H. J/s=W - Unit: K: W/m·C° - **Conductors**: Conduct heat well (metals). Have large conductivities. - **Insulators**: Don't conduct heat well. ## Expansion of Liquids - Don't have a definite shape. - Characterized by its volume - Its expansion is much greater than solids - **Coefficient of apparent expansion**: $\beta = \frac{\Delta V}{V_o \Delta T}$ ## Expansion in Gasses - **Expansion without a change in temperature** - **Expansion without transfer of heat** ## Work in Thermodynamic Processes - Formula: $W = -F \cdot \Delta Y = -P \cdot \Delta A \cdot Y = - P \Delta V$ - $\Delta V = A \cdot \Delta Y$ ## The First Law of Thermodynamics - Formula: $\Delta U = Q - W = \Delta E_0P \Delta V$ - $\Delta U$ = internal energy - $Q$ = energy - $W$ = work ## Thermal Processes - **Isobaric**: constant pressure - **Adiabatic**: no thermal energy transfer, Q = 0. - **Isovolumetric**: constant volume, $\Delta W$ = 0 - **Isothermal**: constant temperature, $\Delta U$ = 0 # Chapter: Adiabatic Processes - **Adiabatic Process**: no energy enters or leaves the system by heat (isolated from its environment). - $\Delta W = \Delta U$. ## Isothermal Process - T → doesn't change. - U → depends only on T. - $\Delta U = 0$. ## Cyclic Process - Returns to the initial state after a series of changes.