Chemistry Exam 2

Units 4 and 5

Energy

the capacity to do work

Work

is movement against force (w= fxd)

Heat

is energy that flows from a hotter to colder object

motion at the molecular level

heat

Temperature

determines that direction of heat flow and is a measure of the average speed of that motion

activation energy

the energy that is needed to start a reaction

isomer

each of two or more compounds with the same formula but a different arrangement of atoms in the molecule and different properties

First law of Thermodynamics

the energy of the universe is instant, or, energy can neither be created nor destroyed; but it can be converted from one form to another

Potential energy

is energy due to position or composition

kinetic energy

energy due to movement

Second Law of thermodynamics

the entropy (chaos) of the universe is increasing

Per capita

accounting for an individual or each person

Countries ranked by co2 emissions

1. china
2. US
3. India
4. Russian Federation
5. Japan
6. Germany

Bond energy

the amount of energy that must be absorbed to break a chemical bond

Bond formation

release of energy via exothermic reaction

Bond breaking

energy is absorbed by bonds via endothermic reaction

Exothermic reactions

energy is released during the course of a chemical reaction

Properties of an exothermic reaction

- Heat/energy is released
- net energy change is negative
- reactants have more potential energy than products

Endothermic reactions

energy is absorbed during the course of a chemical reaction

Properties of an endothermic reaction

- heat/ energy is absorbed
- net energy change is positive
- products have more potential energy than reactants

Uncatalyzed reaction

requires a higher activation energy

catalyzed reaction

requires lower activation energy

Chemical equation for the combustion of hydrocarbons

Hydrocarbon + O2 = CO2 = H2O

EX: CH4 + 2O2 = CO2 +2H2O + energy

Trigonal Planar

120

Linear

180

Bent

104.5

Trigonal pyramidal

107

Tetrahedral

109.5

the largest percentage of energy from the sun comes to the earth is this form

Infrared radiation

Greenhouse gases

gases capable of absorbing and emitting IR radiation thereby warming the atmosphere

Example of Greenhouse gases

- water vapor
- methane
- carbon dioxide
- nitrous oxide
- ozone
- chlorofluorocarbons

Greenhouse effect

Atmospheric gases trap and return a major portion of this heat radiating from the earth through this natural and necessary process. Without this process the Earth would freeze over and be uninhabitable. As the number of atmospheric GHGs increases this process is accelerated causing the Earth's surface temperatures to rise.

Anthropogenic Greenhouse Gases

man made activities that rely on processes that put more carbon atoms into the atmosphere rather than those that remove them; ex: cutting down rainforests, combustion

Classification of Greenhouse Gasses

- 3 or more atoms
- the molecular geometry
- ability to bend and stretch with exposure to the infrared radiation ( without breaking apart )

Ionic compound

metal bonded with nonmetal

Polyatomic ions

two or more atoms covalently bonded together that have an overall positive or negative charge

Dynamic system

natural additional and removal mechanisms

What process adds carbon to the atmosphere?

Respiration

What process removes carbon from the atmosphere?

photosynthesis

Isotopes

atoms of the same element that have the same number of protons but differ in number of neutrons, therefore they have different atomic masses

Average atomic mass

(mass of isotope)(decimal of %) + (mass of isotope)(decimal of %) = Avg. atomic mass

answer should be very similar to atomic weight

Avg. Atomic mass example

Cl35 and Cl37

(35)(.7587) + (37) (.242) = 35.51