What is Chemistry?
Chemistry is the study of matter and its interactions.
We will study the following properties of matter:• composition• properties• interactions• changes
How will matter be studied?
Using the scientific method.
What is the Scientific Method?
Logical approach to exploring a problem or question that has been raised through observation.
Designed to produce a solution or answer that can be tested, retested, and supported by experimentation.
1.State the problem.2.Gather information about the problem.3.Form a hypothesis.4.Test hypothesis.
- variables- controlled experiments
5.Gather and organize data and observations.6.Interpret data.7.Form a conclusion.8.Replication.
What are the steps of the Scientific Method?
What happens to a hypothesis?
Model: An explanation of how phenomena occur and how data or events are related.
Theory: A broad generalization that explains a body of facts or phenomena.
Scientific Law: Statement or mathematical expression about behavior of the natural world.
Use the following terms to organize a Concept Map for matter.
• Can it be separated?• Is composition uniform?• Can it be decomposed by
ordinary chemical means?• Elements• Compounds• Mixtures• Pure Substance• Heterogeneous mixture• Homogeneous mixture
• Air• Stainless steel• Blood• Wood • Water• Sodium chloride• Gold• Oxygen
Matter – anything that has mass and volume.
Matter
How is matter classified? Matter is broken down into two major categories
- Pure Substance- Mixture
- Have unique properties- Cannot be separated by physical means- There are two categories of pure substances:
Elements and Compounds
Pure Substance
Elements - simplest pure substances - contain only one kind of atom - cannot be broken down by physical or chemical means - unique physical and chemical properties
Compounds - substance composed of 2 or more elements that are chemically combined - have unique chemical and physical properties - can be broken down chemically (not physically)
- properties of elements that compounds are broken down into do not resemble properties of original
compound - always break down to the same proportion by mass
Mixtures- Collection of 2 or more pure substances physically mixed together. (No chemical formula)- Properties vary depending on what is in the mixture- Composition can vary (no definite proportion)- There are 2 types of mixtures:
HeterogeneousHomogeneous
Homogeneous Mixture - Substances are distributed evenly throughout the mixture - All regions are identical in their composition and propertiesHeterogeneous Mixture - Substances are not evenly distributed throughout the mixture - Some regions have different properties than others
Matter is described by its properties
Extensive Properties- Depend on how much of a substance there is- Not useful in identifying the substance.
Intensive Properties- Properties that do not depend on size.- Can be useful in identifying the substance.
Physical Properties- Characteristics that can be observed without changing the substance.- Melting point and boiling point are
examplesPhysical Change- Change in a substance that does not involve a change in the identity of the substance.- Phase changes are examples:
solid to liquid - meltingliquid to solid - freezingliquid to gas - vaporizationgas to liquid - condensationsolid to gas - sublimationgas to solid - deposition
Phase Changes are also called changes in state.
There are 4 states of matter: Solid
Liquid
Gas
Plasma
Phase Diagrams
A phase diagram is a graph of pressure versus temperature that shows the conditions under which the phases of a substance exist.
The triple point of a substance indicates the temperature and pressure conditions at which the solid, liquid, and vapor of the substance can coexist at equilibrium.
The critical point of a substance indicates the critical temperature and critical pressure.
Heat of Fusion: The amount of energy as heat required to melt a solid at the solid’s melting point
Heat of Vaporization: The amount of energy as heat that is needed to vaporize a liquid at the liquid’s boiling point at constant pressure
Chemical Properties- characteristics that describe how a substance interacts (or fails to interact) with other substances.
Chemical Change- also called a chemical reaction- change that results in production of 1 or more substances that differ in chemical properties and composition from the original substance
Review Questions1. Matter that has a definite shape and a definite volume is?2. Why is air considered a mixture and not a compound?3. How do compounds differ from mixtures?4. Is each of the following a chemical or physical property?
A. Its mass is 124.3 g.B. It is a shiny solid at room temperature.C. It is easily etched by nitric acid.D. It melts when heated to 670°C.E. It is 31.7 centimeters long.F. It is a good heat conductor.G. It burns in air.H. It is a good conductor of electrical energy
5. Describe the difference between a chemical change and a physical change. Give one example of each kind of
change.