Unit 3 – Chemistry Flashcard

Endothermic
Sometimes also referred to as endergonic or endogonic
Refers to the absorption of energy needs heat to perform reaction)
Means that the energy absorbed is in the form of heat (releases heat in reaction)
Exothermic
Sometimes referred to as exergonic or even exogonic
Means release of energy
Means that the energy released is in the form of heat
Thermochemistry
Is the branch of chemistry that deals with the study of heat changes in chemical reactions and the heats of formation of chemical compounds. It includes heats of reaction, heat capacities and bond energies.
The release of energy is ultimately in the form of
Kinetic energy
Thermodynamics
Is the scientific study of how the transformation of energy by heat can work.
First law of thermodynamics (Law of Conservation of Energy)
In all processes occurring in an isolated system, the energy of the system remains constant. So, energy cannot be created or destroyed, but can only be transformed from one form to another.
Second law of thermodynamics
Energy cannot be transformed from one form to another without a loss of useful energy.
Third law of thermodynamics
The entropy (a measure of a system’s disorder) of a perfect crystal at absolute zero is equal to zero
Zeroth law of thermodynamics
This law is called the Zeroth law because it is fundamental to, and assumed by, the other laws of thermodynamics. It states that if two bodies are each in thermal equilibrium with a third body, then all three bodies are in thermal equilibrium with each other.
chemical reaction has probably occurred when any of the following are observed:
change of colour
heat is released (exothermic)
heat is absorbed (endothermic)
light is produced
a precipitate is formed
a gas is produced (bubbling)
change of smell
Physical
change of state
Nuclear
A change within the nucleus (protons or neutrons)
Radioactivity
Is the spontaneous disintegration of atomic nuclei accompanied by the emission of particles and/or penetrating rays.
Nuclear fusion
Is the process by which light nuclei join to form larger nuclei, releasing tremendous amounts of energy. This process powers the massive energy output of the sun as it converts hydrogen and helium to other heavier elements.
Nuclear fission
Is the process by which a heavy nucleus is split into two smaller nuclei. Neutrons and large amounts of energy are released
Energy
Is a measure of a system’s ability to do work. Various forms include kinetic, potential, electric, chemical, heat, light, sound and nuclear. The symbol for energy is E and its SI units are joules (J).
Heat
Is a form of kinetic energy. Thermal energy (how much kinetic energy the substance has) is the kinetic energy possessed by atoms or molecules moving with random motion within that substance. The symbol for heat that has been absorbed or released is Q and its SI units are joules (J). In most cases we are interested in the heat transferred from one substance to another or the heat released or absorbed in a chemical reaction.
Temperature
Is the degree of “hotness” of a substance. It is a measure of the average kinetic energy of its atoms or molecules. The symbol for temperature is T and its SI units are Kelvin (K). The common units are degrees Celsius.
The Kinetic Molecular Theory
It states that everything is made of tiny particles that are constantly in motion
The kinetic molecular theory makes the following postulates
1. All matter is made up of very small particles, known as atoms or molecules.

2. There are empty spaces between the particles. The distance between particles is large compared to their size.

3. These particles are in constant motion and motion increases with state changes from solid to liquid to gas.

a) The particles in a solid are held close together by strong attractive forces; the particles vibrate but cannot move around independently.

b) The particles in a liquid are held together more loosely by weaker attractive forces; the particles can move around, colliding into other particles and into the container walls.

c) The particles in a gas are very loosely held together by much weaker attraction forces; they can move freely around, filling the entire space available in the container.
4. Their collisions are perfectly elastic, meaning that particles do not lose kinetic energy by colliding with each other.
5. If heat is added to a substance, its particles gain energy and move faster.

Enthalpy
Is defined as the energy of a system which is the sum of the heat (E), and the pressure-volume product (PV).
System
Refers to the particular part of the universe we wish to consider often, that is the contents of beaker or the chemicals reacting within a cylinder of an engine.
Calorimeter
Is the instrument used to study the heat of reaction and the change in enthalpy for reactions with no pressure-volume changes.
Molecular Motion—types of kinetic energy:
Translational energy
Vibrational energy
Rotational energy
Translational energy
Is the type of kinetic energy due to the movement of the whole molecule(this movement is short range and erratic among molecules due to the frequency of collisions with other molecules).
Vibrational energy
Is due to the oscillation or deformation of the bonds within the molecule.
Rotational energy
Is due to the entire molecule rotating
German Henri Hess (1802-1850)
Is primarily recognized for his studies in thermochemistry.
The rate of chemical reactions
1. The nature of the reactant(s)
2. The concentration of the reactant(s)
3. The surface area of the reactants
4. Temperature
5. Pressure. Pressure
6. Effect of a catalyst
There are three mechanisms which help explain how catalysts work:
1. Adsorption
2. Intermediate products
3. Activation energy

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