Chapter 6 Thermochemistry Flashcards
What is energy?
the potential or capacity to move matter.
Kinetic energy. Ek = 1/2mv^2
where m = mass and v = velocity
the energy associated with an object by virtue of its motion. An object of mass and speed or velocity has kinetic energy.
Potential energy. Ep = mgh
where m = mass, g = is the constant acceleration of gravity(9.807m/s^2), and h = height.
is the energy an object has by virtue of its position in a field of force.
Internal energy. Etot = Ek + Ep + U.
where Ek= kinetic energy, Ep = Potential energy and U = internal energy
is the sum of the kinetic and potential energies of the particles making up a substance.
Calorie (cal).
is the common unit of energy. It is defined as the amount of energy required to raise the temperature of one gram of water by one degree Celsius. So,
1 cal = 4.184J
Law of Conservation of Energy
energy may be converted from one form to another, but the total quantity of energy remains constant.
Work, w.
Positive (+) when work is done on a system.
Negative (-) when the system does work on the surroundings.
is an energy transfer (or energy flow) into or out of a thermodynamic system whose effect on the surroundings is equivalent to moving an object through a field of force.
Heat, q.
Positive (+) when a system absorbs heat.
Negative (-) when a system evolves (loses) heat.
is an energy transfer (energy flow) into or out of a thermodynamic system that results from a temperature difference between the system and its surroundings.
The change in internal energy of a system.
is Uf-Ui, the change in internal energy is Ufinal - Uinitial.
First Law of Thermodynamics
states that the change in internal energy of a system
Heat of Reaction
(at a given temperature) is the heat, q, absorbed or evolved from a reaction system to retain a fixed temperature of the system under the conditions specified for the reaction. note: chemical reactions or physical changes are specified depending on the sign of q.
Exothermic Process
is a chemical reaction or a physical change in which heat is evolved (q is negative, energy subtracted).
Endothermic Process
is a chemical reaction or a physical change in which heat is absorbed (q is positive, energy added).
Pressure-Volume Work
w = -P
w, equals the negative of the pressure times the change in volume of the system.
note: w, is defined from the perspective of the system, when
Enthalpy, H.
H = U + PV,
where U is internal energy, P is pressure and V is volume.
is a state function; at constant pressure, the enthalpy change is equal to the heat absorbed or released; enthalpy is an extensive property; the SI unit of enthalpy is Joule (J).
Heat of Reaction, q.
q =
Enthalpy of Reaction a.k.a Enthalpy Change for the Reaction.
the change in enthalpy,
How are the terms enthalpy of reaction and heat of reaction are related?
the change in enthalpy of the system is the heat absorbed or released by a system undergoing a physical or chemical change at constant pressure.
Thermochemical Equations
note:
⇾remember to multiply the value of
is the chemical equation for a reaction (including phase labels) in which the equation is given a molar interpretation, and the enthalpy of reaction for these molar amounts is written directly after the equation.
Heat Capacity, C
q = C
of a sample of substance is the quantity of heat needed to raise the temperature of the sample of substance one degree Celsius (or one Kelvin). Heat capacities are directly proportional to the amount of substance and are listed for molar amounts.
Specific Heat
q = s × m ×
is the quantity of heat required to raise the temperature of one gram of a substance by one degree Celsisu (or one Kelvin) at constant pressure.
Hess’s Law of Heat Summation
states that for a chemical equation that can be written as the sum of two or more steps, the enthalpy change for the overall equation equals the sum of the enthalpy changes for the individual steps.
Standard Enthalpy of Formation a.k.a Standard Heat of Formation
of a substance, is the enthalpy change for the formation of one mole of the substance in its standard state from its elements in their reference form and in their standard states.
Reference Form
an element for the purpose of specifying the formation reaction is usually the stablest form (physical state and allotrope) of the element under standard thermodynamic conditions.
