Energy and Matter

This section continues the basic skills skills section but expands it into the topics of energy, temperature and matter.  You will need to learn this chapter well because this information will be revisited in future chapters and you are expected to be able to recall this information.

Term List

Objectives

1. Name three basic forms of energy.
2. State the law of conservation of energy.
3. Compare the Fahrenheit, Celsius, and Kelvin Temperature Scales
4. Explain what is meant by absolute zero.
5. Name and describe the four states of matter.
6. Compare physical and chemical properties of matter.
7. State the law of conservation of matter.
8. Explain the difference between an element and a compound.
9. Know the name and symbol for the elements on the periodic table.
10. Compare heterogeneous and homogeneous mixtures.
11. Describe several techniques to separate mixtures.

Energy

Energy is the capacity to do work or to produce heat.  Work is the capacity to move an object over a distance against a resisting force.  Work in the scientific sense is not the same as work in the every day sense.  The mathematical equation for work is: W = Force * distance.  Lifting 130 kg from the floor over your head would require a lot of work because you must apply a very large force, once you have lifted the object above your head and the object is now stationary, you are no longer doing any work.  It would be difficult to hold the weight above your head but because the weight is no longer moving, then work is no longer being done.

Forms of Energy

Energy comes in many forms but can be classified into three categories: radiant energy, kinetic energy, and potential energy.

Radiant Energy:  Sunlight is radiant energy.  This energy comes from electromagnetic radiation.  Electromagnetic radiation consists of but not limited to: x-rays, ultraviolet, visible, infrared, and microwaves.  We will discuss this type of energy in a future unit.

Kinetic energy:  Energy of motion.  All objects that are in motion have kinetic energy.  Types of kinetic energy include: mechanical energy and thermal energy.

Potential Energy:  Energy at rest.  Objects have potential energy based on their position.  Water at the top of a water fall has potential energy, because when it falls that energy can be turned into kinetic energy.  This type of energy is called gravitational potential energy.  Electrical potential energy is the energy that exists when objects with different electrical charges are separated.  Energy is required to overcome the force of attraction between the two different charges.  Chemical potential energy exists because of the arrangement of the particles that make up a substance.

Measuring Energy

A common unit of energy is the calorie (cal).  One calorie is the amount of heat needed to raise the temperature of 1 gram of water by 1 Celsius degree.  The energy stored in food is often given a unit that is related to the calorie.  The Calorie (Cal) is the same as exactly 1000 calories or 1 kilocalorie. 

The SI unit of energy is the joule.  The joule is named for James Prescott Joule (1818-1889), an English physicist who made pioneering advances in our understanding of energy.  Joule discovered that mechanical energy is related to heat and therefore the amount of heat produced was related to the amount of energy in the system.  1 cal of heat is equal to 4.184 J of energy.

A calorimeter is used to measure the movement of heat into or out of a substance.  Calorimeters are used to measure the amount of energy in a reaction.  A calorimeter consists of an insulated container (styrofoam cup), a thermometer and a known amount of water.  The reaction is performed in the water or in a small container that is surrounded by the water.  The change in temperature of the water is measured and the amount of energy released or absorbed can be calculated.

Law of Conservation of Energy

The work that Joule did means that different forms of energy are equivalent.  A particular amount of potential or radiant energy can be turned into an exact amount of kinetic energy.  In the process, no energy is lost and no energy is created.

The Law of Conservation of Energy states that in any process energy is neither created nor destroyed.  This law means that energy is transferred from one object to another or from one type of energy to another.  For example, hitting a baseball transfers kinetic energy from the bat to the ball.  Similarly, igniting a match transforms chemical energy into heat and light.

The law of conservation of energy does not apply to processes that occur in the sun and in nuclear reactors.  These processes involve another form of energy called nuclear energy.

Temperature

Temperature is a measure of the warmth or coldness of an object or substance with reference to some standard value.  The measurement of temperature is arbitrary.  What one person says is hot, may be cold to another.  The temperature of the sun's surface is 100 times that of the earth.  We would all agree that the sun is hot, but it would be hard to persuade someone that the desert on a sunny day in July was cold. 

The Fahrenheit and Celsius Temperature Scales

Temperature scales have been developed using the freezing point and boiling point of water as reference points.  Water is very abundant and is very easy to work with.  A thermometer consists of a bulb containing mercury or colored alcohol, attached to a long tube.  The liquid in the bulb expands and contracts with the change in temperature.  A temperature scale is developed by placing the thermometer in ice water and marking the location of the liquid in the tube.  The thermometer is then placed in boiling water and the location of the liquid is marked.  Gabriel Fahrenheit divided the two marks into 180 equal marks.  His scale started at 32 °F and ended at 212 °F.  This is called the Fahrenheit scale.  A Swedish astronomer named Anders Celsius (1701-1744) conducted the same experiment as Fahrenheit, but marked the freezing point 0 °C and the boiling point 100 °C and divided his scale into 100 equal marks.  The Celsius scale is more consistent with the Metric System (base 10) and is therefore used in chemistry.  The problem with both the Fahrenheit and Celsius temperature scales is that they both have negative (-) temperature values.  This can cause problems when you must divide by the temperature.  A new scaled needed to be developed in order to have all positive values.

The Kelvin Temperature Scale

The Kelvin scale is named after the English physicist and mathematician William Thomson, Lord Kelvin (1824-1907).  The Kelvin scale is the SI scale used to measure temperature.  The Kelvin scale is similar to the Celsius scale.  The divisions for both scales are identical, however, the difference is in the location of the zero point.  Lord Kelvin developed the scale while researching the relationship between heat and work.  He defined zero as the point at which there is no heat.  This resolved the issue of negative numbers.  The zero on the Kelvin scale is called absolute zero, or the point at which of particles of matter - their kinetic energy- ceases.  To convert from Celsius to Kelvin you must add 273.  K = °C + 273. 

Matter

When we look at the world around us we see that it is filled with "stuff" - tables, chairs, books, soil, plants, animals, and so on.  Matter is anything that has mass and volume.  This course is primarily concerned with studying the characteristics of matter.

States of Matter

From everyday observations we know that matter exists in three states - solid, liquid and gas.  A fourth state of matter - plasma - is found inside stars.

Solid - A solid holds a particular shape and has a definite volume.  A solid has a orderly arrangement.

Liquid - A liquid does not hold its own shape but it does occupy a definite volume.  A liquid flows freely and takes the shape of its container.

Gas - A gas has no definite shape or volume.  It expands to fill the available volume of its container.

Properties of Matter

Physical Properties - The characteristics of a substance that can be observed without altering the identity of the substance are called physical properties.  Density, color, and melting point are examples of physical properties.

Chemical Properties - The characteristics of a substance that cannot be observed without altering the substance are called chemical properties.  Flammability, which is the tendency of a substance to burn in air, is a chemical property.

Changes in Matter

Physical Changes - Changes which do not alter the identity of the substance are called physical changes.  Crushing, tearing, and changes in state are examples of physical changes.

Chemical Changes - Changes which alter the identity of the substance are called chemical changes.  Burning, cooking, rusting are all examples of chemical changes.

Conservation of Matter

Matter, like energy, is neither created nor destroyed in any process.  Antoine Lavoisier (1743-1794) performed many experiments to prove that matter was conserved during a chemical reaction.  Lavoisier used a balance to measure the amount of matter before and after a reaction.  It was through his careful measurements that the Law of Conservation of matter came to be and it applies throughout the universe, in all branches of science.

Elements and Compounds

Early thinkers believed that the variety of substances we see around us is actually the result of combinations of just a few simple forms of matter.  These forms were called elements.  The thinkers had identified four elements: earth, wind, water and fire.  It was from these four elements that all matter on earth was made.

Elements

Our understanding of what defines a chemical element has changed radically since ancient times, but the basic concept of a fundamental kind of matter has endured.  An element is a substance that cannot be separated into simpler substances by a chemical change.  We have identified over 104 elements that make up all of the matter in the universe.

Elements are named after famous scientists, countries, states, and even planets.  Chemical elements have abbreviations, called element symbols.  Element symbols consist of one or two letters.  The first letter is always capitalized, and the second, if present, is lower case.  Some elements, such as hydrogen, have symbols straight from the English name.   

Scientists develop a table to organize the elements in a logical, orderly fashion.  This table is called the periodic table of elements and is essential to the study of chemistry.

Compounds

A compound forms from the combination of two or more elements in a fixed proportion.  The millions of compounds that exist in the universe are formed from the elements on the periodic table.  When magnesium burns in the presence of oxygen a compound called magnesium oxide forms.  Magnesium oxide is composed of 60.32 percent magnesium and 39.68 percent oxygen.  Magnesium oxide always forms in these fixed proportions.  Chemists do not usually write the names of the compounds, but write the symbols called formulas.  The chemical formula for magnesium oxide is MgO.

Distinguishing Between Elements and Compounds

Elements and compounds are pure substances.  Every pure substance has a unique set of physical and chemical properties.  Elements react to form compounds and compounds can be divided into individual elements.  Dividing a compound into elements require it to be torn apart through a process.  Electrolysis uses electricity to divide compounds into elements.  Water can be divided into hydrogen and oxygen through electrolysis.

Mixtures

A mixture is a blend of two or more pure substances.  A heterogeneous mixture is one in which the parts are clearly visible.  A piece of granite is an example of a heterogeneous mixture.  A homogeneous mixture is one in which the parts are not clearly visible.  Air is an example of a homogeneous mixture because the oxygen, nitrogen and carbon dioxide are all colorless and are indistinguishable.  To determine whether a substance is a mixture, you first have to separate it into two or more pure substances.

Separating the Components of a Mixture

Special equipment and techniques have been developed to separate mixtures into their pure substances.

1. Filtration:  A piece of paper, or other porous solid, is used to separate liquids from the solids.  The liquid part of the mixture passes through the paper, while the solids are collected on the paper.  This method is used to separate heterogeneous mixtures.
2. Distillation:  Distillation is used to separate homogeneous mixtures.  The mixture is separated based on the boiling points of the components.  The water and salt in sea water are separated by boiling the water.  The clean water is collected and the salt, which has a much lower boiling point, is left behind.  Crude oil is separated into its components by a process called fractional distillation.
3. Crystallization:  This method is used to produce solids of very high purity.  Gemstones are crystals that formed as our young planet slowly cooled.
4. Chromatography:  A solution can be separated by allowing it to flow slowly over a stationary surface.  The different components flow at different rates because they interact with the stationary surface differently.  Mixtures of gases, liquids, and solids can be separated by chromatography.  Chromatography is the most powerful tool chemists have to separate a homogeneous mixture into its pure substances.

Matter and Energy

The relationship between matter an energy is such that you can't have one without the other.  Matter stores energy inside its bonds and releases it during chemical reactions.  Energy is required to form new bonds and that energy is stored.  The energy from the sun is the result of the transformation of hydrogen into helium.  Through the process of nuclear fusion, all of the known elements in the universe were produced.