CHEMICAL INTERACTIONS Chapter 1 - Chemical Reactions Outline/Review

1.1 Matter and Its Changes CHEMISTRY is the study of the properties of matter and how matter changes. An ELEMENT is a substance that cannot be broken down into any other substances by chemical or physical means. All the matter around you is composed of one element or a combination of two or more elements.

A COMPOUND is a substance made of two or more elements chemically combined in a specific ratio. An example of a compound is CO 2 A MIXTURE is made from two or more elements or compounds in the same place but not forming new material. A SOLUTION is a well-mixed mixture where substances are not easily seen.

Chemistry is the study of the kinds of and changes in matter. A PHYSICAL CHANGE is when the form or appearance of a material changes. An example of a physical change is water in the forms of ice, water, and water vapor. A CHEMICAL CHANGE is when a new substance is produced. An example of a chemical change is metal rusting.

The change of font type is an example of a physical change. Changing what something says is an example of a chemical change. You can observe a chemical reaction by observing changes in the properties of matter. A PRECIPITATE is a solid formed during a chemical reaction.

production of a gas precipitation of a solid a change in temperature (either up or down) a color change change in physical properties Some of the evidence for chemical reactions is:

The smallest particle of an element is an ATOM. A MOLECULE is the combination of two or more atoms. An example of a molecule is H 2 O An example of an atom is H A CHEMICAL BOND is the force that holds atoms and molecules together. Chemical reactions occur when chemical bonds are either formed or broken apart.

Therefore, to summarize... Matter may be in the form of elements, compounds, or mixtures. Chemical changes result in the formation of new substances. Color change, production of a gas or a precipitate, a change in temperature, or a change in the properties of a substance are all clues that a chemical reaction has taken place. Chemical reactions occur when chemical bonds are formed or broken

1.2 Describing Chemical Reactions A CHEMICAL EQUATION is a shorter, easier way to show chemical reactions. Most elements are represented by a 1-2 letter symbol. An example of a symbol is O for oxygen. A compound is represented by a “word”, called a CHEMICAL FORMULA. An example of a chemical formula is H 2 O. A SUBSCRIPT shows the number of atoms of an element in a molecule.

The materials you have at the beginning of a reaction are the REACTANTS. The materials you have at the end of a reaction are called the PRODUCTS. A chemical equation uses symbols to show the reactants and products of a chemical reaction. An example of a chemical reaction is: (H 2 and O 2 are the reactants while H 2 O 2 is the product.) H 2 + O > H 2 O 2

All the atoms present at the start of a reaction are present at the end. The law of conservation of mass states: The amount of matter in a chemical reaction does not change, so the total mass of the reactants must equal the total mass of the products. A balanced chemical equation has the same amount of atoms for the reactants and the products. A COEFFEICIENT can be added to balance the number of atoms in an equation.

An example of a balanced equation is: 2 Mg + O > 2 MgO Many reactions can be classified in one of three categories: SYNTHESIS DECOMPOSITION REPLACEMENT

A SYNTHESIS reaction occurs when two or more substances combine to make a more complex compound. An example of a synthesis reaction is: 2 SO 2 + O H 2 O -----> 2 H 2 SO 4 A DECOMPOSITION reaction breaks down compounds into simpler products. An example of a decomposition reaction is: 2 H 2 O > 2 H 2 O + O 2

A REPLACEMENT reaction is when one element replaces another in a compound OR when two elements trade places. Examples of two replacement reactions are: 2 CuO + C -----> 2 Cu + CO 2 MgCl 2 + K 2 S -----> MgS + 2 KCl

Therefore, to summarize... A chemical equation uses symbols to show the reactants and products of a chemical reaction. Matter is neither created nor destroyed during a chemical reaction. Chemical reactions may be classified by the types of changes in reactants and products.

1.3 Controlling Chemical Reactions Every chemical reaction involves a change of energy. Some reactions release energy and others absorb energy. An EXOTHERMIC reaction releases energy in the form of heat. An ENDOTHERMIC reaction absorbs energy and feels cold. ACTIVATION ENERGY is the amount of energy needed to get a reaction started.

The rate of a reaction is affected by such factors as concentration, surface area, and temperature. Increasing the CONCENTRATION is one way to increase the rate of a reaction. Increasing the SURFACE AREA is another way of speeding up a reaction. Increasing the TEMPERATURE is a third way to speed up a reaction. A CATALYST is a material that lowers the activation energy needed to start the reaction.

A type of biological catalyst is an ENZYME. Enzymes provide a surface for the reactions to take place. An INHIBITOR is a material used to slow down a reaction - often to make it less dangerous.

Therefore, to summarize... Every chemical reaction involves a change in energy. Some reactions absorb energy and others release it. The rate of a chemical reaction can be controlled by such factors as concentration, surface area, temperature, and use of a catalyst or inhibitor.

1.4 Fire and Fire Safety The rapid reaction between oxygen and a fuel is called COMBUSTION. A FUEL is a material that releases energy when it burns. Three things are necessary to start and maintain a fire--fuel, oxygen, and heat. Water removes two parts of the fire triangle--heat and oxygen.

Some of the most common sources of fires are small heaters, kitchen fires, faulty electrical wiring, and carelessness with cigarettes (the most deadly). Use baking soda to put out a fire that starts on the stove. Try to extinguish small fires yourself, but leave a growing fire to the fire department. Prevention is the best form of fire safety.

Therefore, to summarize... The fire triangle shows the three things necessary to start a fire and keep it burning: fuel, oxygen, and heat. Water stops combustion by keeping the fuel from coming in contact with oxygen. Also, evaporation of water uses a great deal of heat and cools the fire.

This concludes the Chapter 1 review for the Chemical Interactions book. STUDY WELL!