Chemistry Chapters 5 and 6

Diffusion

the process by which gas particles spread out in a container from an area of higher concentration to an area of lower concentration

mean free path

the distance a gas particle travels between collisions

Effusion

occurs when a gas escapes from its container through a small hole into a vacuum

What two factors must be taken into consideration to describe the behavior of a real gas

1) the finite volume or size of the particles

2) the effect of intermolecular forces (the attraction or repulsion between the particles)

Energy

an extensive property observed in physical systems as the capacity to do work or transfer heat

Work (w)

the energy required to move an object over a specified distance (d) by applying a force (F)

Heat (q)

the transfer of energy between two bodies that arises from a difference in temperature

thermochemistry

the branch of chemistry focused on quantifying heat exchanges involved in chemical and physical changes 

Joule (J)

the SI unit for energy is the…

Potential Energy (Ep)

is the energy stored in an object because of its position or composition

Kinetic Energy (Ek)

is the energy associated with an object’s motion

Chemical Energy

is a form of potential energy stored in atoms and molecules because of the position of their electrons and atomic nuclei

Thermal Energy 

is kinetic energy associated with the random motion of molecules, ions, or atoms and results in a system’s temperature

Gravitational energy

is a type of potential energy

Specific energy

is defined as a substance’s energy per unit mass when burned in excess oxygen

Kinetic energy

is the energy that arises because of an object’s motion

The Law of Conservation of Energy

states that energy is neither created nor destroyed. Rather, it is converted from one form to another

Thermodynamics

is the study of the transfer of heat and other types of energy during a chemical or physical process

System

a process of interest or a part of the universe being studied 

Surroundings

everything outside the system that can interact with it, exchanging energy or matter

open system

exchanges matter and energy with the surroundings

closed system

exchanges energy, but not matter with the surroundings

isolated system

is insulated and DOES NOT exchange matter or energy with the surroundings

exothermic

heat (q) flows from the system into the surroundings q<0

endothermic 

heat (q) flows from the surroundings into the system q>0

Internal energy (U)

is the sum of the kinetic and potential energy components contained within a system

what is a state function?

a property determined only by the state of the system, not on how the system achieved that state 

what are examples of state functions

mass, pressure, temperature, volume, energy

The First Law of Thermodynamics

states that the total amount of energy in the universe is constant

Heat Capacity (C)

is the amount of heat needed to increase a system’s temperature by 1 degree Celsius

Specific Heat Capacity (s)

is the amount of heat necessary to raise the temperature of 1 g of a substance by 1-degree Celsius 

Pressure-volume work (PV-work) 

occurs when a volume change produces a force that acts against an opposing external pressure

Why is enthalpy important?

1) many chemical reactions occur under conditions of constant pressure

2) many chemical reactions do not involve gases and thus there is little if any, pressure change or gas volume changes 

3) in many reactions, particularly those involving no change in gas volume, the enthalpy change approximates the total energy change since pressure-volume work is minimal 

4) in chemical reactions in which there is a change in the number of moles of gas, the amount of heat transferred is usually much larger than the amount of work done 

Calorimetry

the measurement of heat transfer in a chemical or physical process. it is used to determine the amount of heat absorbed or released by a substance, typically by measuring temperature changes in a controlled environment, such as a calorimeter

Bomb Calorimetry

a constant volume device. the heat transferred in bomb calorimetry experiments is equivalent to the change in internal energy

Coffee-cup Calorimetry

is a constant pressure device. the heat transferred in coffee-cup calorimetry is equal to the change in enthalpy 

Thermochemical Equation

a balanced chemical equation that includes the heat of reaction is called a thermochemical equation

Standard State

a reference point that describes the physical state in which a substance exists at 1 bar pressure and a stated temperature 

Standard Enthalpy of Formation

the change in enthalpy when 1 mol of a compound is formed directly from its constituent elements in their standard states