Humboldt State University ® Department of Chemistry

Richard A. Paselk

	Science 331
Fall 2004	Lecture/Activity	Office: SA560a
Notes: 25 August		Phone: x 5719 Home: 822-1116
		e-mail: rap1

Safety

Safety Lecture and Quiz

Elements Exercise

HSU has one of the few display collections of "large" samples of all of the elements with non-radioctive forms (isotopes). Using this display determine the following at "room temperature and pressure":

• How many elements are gaseous?
• How many elements are liquid?
• How many elements are colored? (For this exercise consider white, silver, grey and black to have no color.)
  • List the colored elements and their colors.
• What is the highest number for a non-radioactive element?
  • How many elements are non-radioactive?
• How many elements would you gues are metals?

What is Chemistry?

Why Chemistry is often considered the "central science." Examples.

Chemistry is the study of matter and its transformations.

• "Classical" chemistry involves mostly electron transfers and/or interactions of charges (electron and nuclear). As we'll see only some electrons in atoms are involved - the outer or valence electrons of atoms.
• Nuclear chemistry is an extension of chemistry where nuclei are transformed changing one kind of atom (element or isotope) to another. This is a completely separate realm of phenomena, largely unimportant in everyday life (unless you work at a nuclear power plant!) and we will not cover it.

More specifically, chemistry is the scientific study of matter. So what do we mean by science? Two common "definitions":

• The body of knowledge and rules/laws/theories we have discovered regarding the natural world.
• The method of discovery and confirmation used by scientists. Classically we describe this process as the "Scientific Method" summarized in the steps below:
  • Identify a problem based on initial observations
  • Collect data via planned Observations and/or Experiments ("asking nature a question")
    • "Clean" simple experiments vs. statistical inference
    • Controls - everything the same except the variable of interest.
  • Analyze and Evaluate results
  • Hypothesis
  • Theory (model)
    • Law

Let's look at a couple of chemical problems:

• H₂ balloons
• Candle flame.

Matter

What is matter? Stuff. Has mass and occupies space.

Mass: The measure of quantity for matter. Mass is the property of matter resulting in its inertia and and attraction via gravity.

• Do not confuse mass and weight. Weight is the force acting on an object due to gravity. We often interchange these terms in conversation, but they are quite different - you have the same mass whether you are weightless in space on here on Earth (taking a shuttle flight is no substitute for a diet!). To confuse us further we call the determination of mass "weighing"!

What is matter? Stuff. Has mass and occupies space.

Mass: The measure of quantity for matter. Mass is the property of matter resulting in its inertia and and attraction via gravity.

• Do not confuse mass and weight. Weight is the force acting on an object due to gravity. We often interchange these terms in conversation, but they are quite different - you have the same mass whether you are weightless in space on here on Earth (taking a shuttle flight is no substitute for a diet!). To confuse us further we call the determination of mass "weighing"!

Matter has both physical properties and chemical properties. These are properties which do not depend on the quantity of substance and therefore they can be used to identify a substance (sometimes referred to as intensive properties).

• Physical properties of substances can be observed without, in principle, changing their compositions. Physical properties include mass, color, , density etc. Note that physical changes such as melting, cutting, etc. do not change composition.

States of Matter. Matter can exist in three states under earth-surface conditions:

• Solid: definite shape and volume (Crystals vs. super-cooled liquids or glasses)
• Liquid: definite volume, but no defined shape - will fit to container etc.
• Gas: no definite shape or volume - will fill whatever container they are in.
  • both liquids and gases are fluids.

A fourth state of matter commonly occurs under special conditions: a plasma. A plasma is an ionized fluid - can be contained by magnetic fields.

• Chemical properties of substances describe behaviors which lead to changes in composition. Chemical properties describe reactivity under various circumstances (does it burn in air, react with acids or bases, corrode in sea water etc.) Note that chemical changes result in different compositions.

Conservation Laws

Law of Conservation of Mass: Mass is neither created nor destroyed during a chemical change. (Strictly speaking there is no measurable change.) For example, if we burn gasoline (octane) in air we will get carbon dioxide and water:

If we were to weigh (determine the mass) of the carbon and oxygen vs. the carbon dioxide and water we would find them to be identical - the masses are the same on both sides of the equation (that's why its called a chemical equation, the two sides indicate are equal). Looked at another way, if you count the atoms, the numbers of each kind of atom on each side are identical - so we can also say that atoms are conserved in chemical processes.

Law of Conservation of Energy: Energy is neither created nor destroyed in chemical processes.

Problem here of course is- What is energy? Energy is the capacity to do work. So what's work? Work occurs when an object (mass) is moved against a force. Some common forms of energy important to our study include:

• Kinetic Energy (KE) - energy due to motion. KE = 1/2 mv².
• Potential Energy (PE) - energy due to position.

Another form of energy we need to be familiar with is:

• Heat - energy transferred between objects because of a difference in temperature.
  • Heat vs. Temperature: heat tells us how much energy is held (can be transferred from) and object or given mass of stuff. Temperature on the other hand is a measure of the energy per particle in a sample of matter. Thus for a gas temperature is a measure of the average Kinetic Energy (KE) of the gas particles, while the amount of energy we must add to the gas to achieve this average KE is the heat.
  • Note that most energy eventually ends up as heat (ex.: burning gasoline to move a car - heat in exhaust, friction in tire deformation, braking, etc.) or work (car is moved against its inertia).

Note that these forms of energy are readily interconverted.

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© R A Paselk

Last modified 25 August 2004