Chemistry Chapter 7

Energy

Something that matter possesses by virtue of an ability to do work.

Kinetic Energy (KE)

Energy of motion. KE=1/2mv^2

Potential Energy (PE)

Stored energy

Chemical Energy

The potential energy of chemicals that is transferred during chemical reactions.

Law of Conservation of Energy

The energy of the universe is constant; it can be neither created nor destroyed but only transferred and transformed.

Heat

Energy that flows from a hot object to a cold object as a result of their differences in temperature.

Thermal Energy

The molecular kinetic energy possessed by molecules as a result of the temperature of the sample. Energy that is transferred as heat.

joule (J)

The SI unit of energy.

kilojoule (kJ)

1000 J

calorie (cal)

4.184 J. The energy that will raise the temperature of 1.00g of water from 14.5 to 15.5 degrees Celsius.

kilocalorie (kcal)

1000 cal. The nutritional calorie with a symbol of (C).

Thermal Equilibrium

A condition reached when two or more substances in contact with each other come to the same temperature.

Internal Energy (IE)

The sum of all of the kinetic energies and potential energies of the particles within a system.

Molecular Kinetic Energy

The energy associated with the motions of and within molecules as they fly about, spinning and vibrating.

Kinetic Molecular Theory

Molecules of a substance are in constant motion with a distribution of kinetic energies at a given temperature. The average kinetic energy of the molecules is proportional to the Kelvin temperature.

State

The set of specific values of the physical properties of a system-its composition, physical form, concentration, temperature, pressure and volume.

State Function

A quantity whose value depends only on the initial and final states of the system and not on the path taken by the system to get from the initial to the final state. (P, V, T, H, S and G are all state functions.)

Boundary

The interface between a system and its surroundings across which energy or matter might pass.

System

That part of the universe under study and separated from the surroundings by a real or an imaginary boundary.

Surroundings

The part of the universe other than the system being studied and separated from the system by a real or imaginary boundary.

Universe

The system and surroundings taken together.

Adiabatic Change

A change within a system during which no energy enters or leaves the system.

Heat Capacity

The quantity of heat needed to raise the temperature of an object by 1 degree Celsius.

Specific Heat

The quantity of heat that will raise the temperature of 1 g of a substance by 1 degree Celsius, usually in units of cal or J.

Molar Heat Capacity

The heat that can raise the temperature of 1 mol of a substance by 1 degree C; the heat capacity per mole.

Exothermic

Descriptive of a change in which energy leaves a system and enters the surroundings.

Endothermic

Descriptive of a change in which a system's internal energy increases.

Heat of Reaction

The heat exchanged between a system and its surroundings when a chemical change occurs within a system.

Calorimeter

An apparatus used in the determination of the heat of a reaction.

Calorimetry

The science of measuring the quantities of heat that are involved in a chemical or physical change.

Pressure

Force per unit area.

Atmospheric Pressure

The pressure exerted by the mixture of gases in our atmosphere.

Bar

The standard pressure for thermodynamic quantities; 1 bar = 105 pascals, 1 atm = 101,325 Pa.

Expansion Work

The energy transferred as work when a system expands or contracts against the pressure exerted by the surroundings. At constant pressure, w = -P x delta(V).

First Law of Thermodynamics

A formal statement of the law of conservation of energy. delta(E) = q + w.

Heat of Combustion

The heat involved in the combustion of a substance.

Heat of Reaction at Constant Volume (qv)

The heat of a reaction in a sealed vessel, like a bomb calorimeter, delta(E).

Heat of Reaction at Constant Pressure (qp)

The heat of a reaction in an open system,

Enthalpy (H)

The heat content of a system.

Enthalpy Change

The difference in enthalpy between the initial state and the final state for some change.

Standard State

The condition in which a substance is in its most stable form at 25 degrees Celsius and 1 atm.

Standard Heat of Reaction (?H�)

The enthalpy change of a reaction when determined with reactants and products at 25 �C and 1 atm and on the scale of the mole quantities given by the coefficients of the balanced equation.

Thermochemical Equation

A balanced chemical equation accompanied by the value of ?H� that corresponds to the mole quantities specified by the coefficients.

Enthalpy Diagram

A graphical depiction of enthalpy changes following different paths from reactants to products.

Hess's Law

For any reaction that can be written in steps, the standard heat of reaction is the same as the sum of the standard heats of reaction for the steps.

Standard Heat of Combustion

The enthalpy change for the combustion of one mole of a compound under standard conditions.

Fuel

Commonly one component of a combustion reaction; specifically the reducing agent.

Standard Enthalpy of Formation (?Hf�)

The amount of heat absorbed or evolved when one mole of the compound is formed from its elements in their standard states.