Thermodynamics (Physics) UWorld

Heat Transfer

Heat is transferred from one location to another by conduction, convection, or radiation.

Conduction

Intermolecular collisions cause the movement of heat between high and low temperatures regions because molecules with high temperatures move faster and have higher kinetic energies. High speed molecules impart kinetic energy with slow molecules and transfer thermal energy

Rate of heat transfer through conduction:

depends on thermal conductivity of a substance. Objects at the same temperature with different thermal conductivity are perceived to be different temperatures. Objects with high thermal conductivity feel cold and thermal insulators feel warm.

Deposition

Changing from a gas to a solid

Thermodynamic Equibrium

If the temperature of the system is constant and uniform throughout its volume and there is no flow of energy, A system and its surroundings have the same temperature at thermodynamic equilibrium.

State Functions

The equilibrium state of a relationship between various thermodynamic variables and are independent of the path taken by a system to arrive to its present state. When I feel Dense and Under Pressure I watch TV and get HUGS

Process Functions

The path taken by a system to transition from one equilibrium system to another. A system transitions from one state to another due to a net flow of energy in the form of heat transfer and work. Work is a process function.

Isothermal

Process in which temperature of the system does not change

Adiabatic

Process in which there is no heat exchange between the system and environment

Isochoric

Process in which volume of the system does not change

Isobaric

Process in which pressure of the system does not change

Change in Internal Energy

Delta U = Q + W

Delta U = Internal Energy, Q = The sum of the amount of heat transferred to the system W = Work done by the system

If there is no direct heat transfer Q = 0

W = - P Delta V

Conduction

Transfer of heat through direct physical contact

Convection

The transfer of heat through the flow of fluid. Fluids absorb heat from hotter regions and deliver it to colder regions.

Radiation

Transfer of heat through electromagnetic radiation such as infrared lights. Is significant only for high temperatures.

Specific Heat

The amount of heat required to change the temperature of a unit of mass by 1 degree

Heat Capacity C Equation

C = mc = q / Delta T

q = C Delta T = m c Delta T

C = heat capacity

c = specific heat

Phase Transition

Matter exist in three phases: solid, liquid, and gas. During a phase transition, the temperature of a substance remains constant (straight lne on a graph). The condensation point is the temperature at which the phase transition from gas to liquid, releasing heat equal to its latent heat of vaporization.

Calorimetry Equation (Thermally Insulated)

If thermally insulated, q of water can be solved using m c Delta T and that q is plugged in for the m c Delta T of the object in the equation when solving for c.

Phase Transitions

During phase transitions, the temperature of a substance remains constant. A liquid at the exact same temperature of its boiling point is transitioning from a liquid to a gas. It must gain an amount of heat equal to its heat of vaporization before all the liquid turns to gas and the temperature increases.

Enthalpy Delta H

A measure of bond energy, and a change in the enthalpy of the reaction results in the release or absorption of heat. Energy is released as heat if the enthalpy of the products is lower than the reactants and Delta H is negative (exothermic). Temperature of the (surroundings) increases then Delta H is negative/exothermic.

Entropy Delta S

Measure of a disorder and is highest in gases and lowes tin solids. Delta S is positive if reaction is more disordered (solid to gas)

Thermal Expansion

The length/volume of a substance is linearly proportional to its temperature

Delta L = a L Delta T

Delta V = a V Delta T

Thermal expansion is proportional to temperature

Calorimetry Equation (kJ)

m c Delta T = q gives the answer in cal. Can be converted to kJ by using 4.2 kJ / 1000 cal

Sublimation

Phase change of solid to gas

Latent Heat of Fusion

Phase change from a solid to a liquid requires heat (energy) to break bonds between molecules, this energy is the latent heat of fusion. When heat is added to a mixture of ice and water at 0 degrees , the heat will first melt the ice before raising the temperature of water.

Closed System

If temperature of surroundings (water) increases than heat can be exchanged but if it is enclosed than matter cannot be exchanged making it a closed system.

Isolated System

Heat and matter cannot be exchanged, (completely thermaly isolated)