Table of Contents Chapter Preview 6.1 Observing Chemical Change 6.2 Describing Chemical Reactions 6.3 Controlling Chemical Reactions 6.4 Fire and Fire Safety

Chapter Preview Questions 1. Which of the following is an example of a physical change? a. Wood burns and becomes ash. b. A silver fork tarnishes. c. Water boils and becomes water vapor. d. Leaves decay over time.

Chapter Preview Questions 1. Which of the following is an example of a physical change? a. Wood burns and becomes ash. b. A silver fork tarnishes. c. Water boils and becomes water vapor. d. Leaves decay over time.

Chapter Preview Questions 2. When a forest burns, it a. neither absorbs nor releases energy. b. loses matter and energy. c. absorbs energy. d. releases energy.

Chapter Preview Questions 2. When a forest burns, it a. neither absorbs nor releases energy. b. loses matter and energy. c. absorbs energy. d. releases energy.

Chapter Preview Questions 3. Fe, which stands for iron, is a a. chemical symbol. b. chemical equation. c. atomic number. d. name.

Chapter Preview Questions 3. Fe, which stands for iron, is a a. chemical symbol. b. chemical equation. c. atomic number. d. name.

Chapter Preview Questions 4. The ease and speed with which an element combines with other elements is called its a. atomic number. b. chemical property. c. physical property. d. reactivity.

Chapter Preview Questions 4. The ease and speed with which an element combines with other elements is called its a. atomic number. b. chemical property. c. physical property. d. reactivity.

What happens during a chemical reaction? Suppose you fill a sealable bag with ice cubes, and you allow the ice to melt. How would the mass of the bag and ice before melting compare to the mass of the water and the bag after melting? Explain your answer.

Section 1: Observing Chemical Change Standard 8.5.a: Students know reactant atoms and molecules interact to form products with different chemical properties. Standard 8.5.c: Students know chemical reactions usually liberate heat or absorb heat.

Matter and Change How can changes in matter be described? Physical Property Chemical Property Changes in matter can be described in terms of physical changes and chemical changes A characteristic of a substance that can be observed with out changing into another substance. A characteristic of a substance that describes its ability to change into other substances.

Matter and Change Physical Change Any change that alters the form or appearance of a substance but does not make the substance into another substance.

Matter and Change Chemical Property A characteristic of a substance that describes its ability to change into other substances.

Properties and Changes in Matter Chemical changes occur when bonds break and new bonds form.

Evidence for Chemical Reactions How can you tell when a chemical reaction occurs? Precipitate Endothermic Reaction Exothermic Reaction Chemical reactions involve changes in properties and changes in energy that you can observe. A solid that forms from solution during a chemical reaction. The making and breaking of bonds results in a net absorption of energy The making and breaking of bonds results in a net release of energy.

Evidence for Chemical Reactions How can you tell when a chemical reaction occurs? 4 Observations of Chemical Change There is a formation of gas which can be seen by a fizzing or bubbling. The reaction will cause heat, light, or odor to be emitted A color change is produced. A solid is formed during the change.

Section 1 Quick Quiz What happens when chemical bonds break and new bonds form? A physical change A chemical reaction Matter is destroyed Surface area increases Answer: B – A chemical reaction

Section 1 Quick Quiz A chemical reaction that absorbs energy in the form of heat is described as endothermic exothermic combustion unbalanced Answer: A - endothermic

Section 1 Quick Quiz Every chemical reaction involves a change in mass energy concentration state Answer: B - energy

Section 1 Quick Quiz One example of a chemical change is filtering burning wood boiling water crushing a can Answer: B – burning wood

Section 1 Quick Quiz Anything that has mass and takes up space is considered matter energy chemistry endothermic Answer: A - matter

Energy in Chemical Changes A student places two substances in a flask and measures the temperature once per minute while the substances react. The student plots the time and temperature data and creates the graph at left.

Energy in Chemical Changes Reading Graphs: What was the temperature in the flask at 3 minutes? When was the first time the temperature was at 6ºC? At 3 minutes the temperature in the flask was about 30ºC. The first time the temperature was 6ºC was at about 7 minutes.

Energy in Chemical Changes Calculating: How many degrees did the temperature drop between 2 minutes and 5 minutes? About 20ºC

Energy in Chemical Changes Interpreting Data: Is the reaction endothermic or exothermic? Explain. The reaction was endothermic, because it absorbed thermal energy from the reaction mixture, causing the temperature to drop.

Energy in Chemical Changes Inferring: At what temperature did the reaction stop? How can you tell? The reaction stopped at about 2ºC. You can tell because that is the lowest temperature reached.

Energy in Chemical Changes Drawing Conclusions: Suppose the temperature in the flask increased instead of decreased as the reaction occurred. In terms of energy, what kind of reaction would it be? Explain. If the temperature increased instead, the reaction would be exothermic, because an exothermic reaction is one in which energy is released.

Section 2: Describing Chemical Reactions Standard 8.5.b: Students know the idea of atoms explains the conservation of matter. In chemical reactions the number of atoms stays the same no matter how they are arranged, so their total mass stays the same.

What Are Chemical Equations? What information does a chemical equation contain? Chemical equations use chemical formulas and other symbols instead of words to summarize a reaction.

Conservation of Matter The principle of conservation of matter states that in a chemical reaction, the total mass of the reactants must equal the total mass of the products.

Balancing Chemical Equations To describe a reaction accurately, a chemical equation must show the same number of each type of atom on both sides of the equation.

Balancing Chemical Equations Magnesium (Mg) reacts with oxygen gas (O2), forming magnesium oxide (MgO). To write a balanced equation for this reaction, first write the equation using the formulas of the reactants and products, then count the number of atoms of each element.

Balancing Chemical Equations Balance the equation for the reaction of sodium metal (Na) with oxygen gas (O2), forming sodium oxide (Na2O).

Balancing Chemical Equations Balance the equation for the reaction of tin (Sn) with chlorine gas (Cl2), forming tin chloride (SnCl2).

Balancing Chemical Equations http://education.jlab.org/elementbalancing/index.html

Classifying Chemical Reactions Many chemical reactions can be classified in one of three categories: synthesis, decomposition, or replacement.

Section 2 Quick Quiz CaCO represents a chemical symbol. subscript. formula. reaction. Answer: C - formula

Section 2 Quick Quiz A chemical equation that shows the same number of each kind of atom on both sides of the equation is said to be balanced. unbalanced. an incomplete reaction. a replacement reaction. Answer: A - balanced

Section 2 Quick Quiz A bottle of hydrogen peroxide that eventually turns into a bottle of water and oxygen gas is an example of a replacement reaction. precipitate reaction. decomposition reaction. synthesis reaction. Answer: C - decomposition

Section 2 Quick Quiz The substances listed on the left side of a chemical equation are the coefficients. products. reactants. precipitates. Answer: C - reactants

Section 2 Quick Quiz In a chemical equation, numbers often appear in front of a chemical formula. These numbers tell you the number of molecules in each atom in the reaction. number of molecules or atoms of each substance in the reaction. number of elements in the reaction. number of atoms in each molecule in the reaction. Answer: B – number of molecules or atoms of each substance in the reaction

Section 3: Controlling Chemical Reactions Standard 8.5.a: Students know reactant atoms and molecules interact to form products with different chemical properties. Standard 8.5.c: Students know chemical reactions usually liberate heat or absorb heat.

Energy and Reactions How is activation energy related to chemical reactions? Activation Energy Potential Energy Kinetic Energy All chemical reactions require a certain amount of activation energy to get started. The minimum amount of energy needed to start a chemical reaction. Stored energy that results from the position or shape of an object. Energy that an object has due to its motion.

Energy and Reactions All chemical reactions require a certain amount of activation energy to get things started.

Energy and Reactions Exothermic Reaction Endothermic Reaction A reaction that releases energy in the form of heat. A reaction that absorbs energy in the form of heat.

Energy and Reactions Both exothermic and endothermic reactions need energy to get started.

Rates of Chemical Reactions Factors that affect rates of reaction include: surface area; temperature; concentration; and the presence of catalysts and inhibitors. A material that increases the rate of reaction by lowering the activation energy. A material used to decrease the rate of reaction. Biological catalysts found in the cells of the body. What factors affect the rate of a chemical reaction? Catalyst Inhibitor Enzyme

Rates of Chemical Reactions The cells in your body (as in all living things) contain biological catalysts called enzymes. After a reaction, an enzyme molecule is unchanged.

Section 3 Quick Quiz The minimum amount of energy that has to be added to start a reaction is the exothermic energy. endothermic energy. activation energy. chemical energy. Answer: C – activation energy

Section 3 Quick Quiz Chemicals that act as biological catalysts by speeding up reactions in living things are enzymes. inhibitors. reactants. fuels. Answer: A - enzymes

Section 3 Quick Quiz A material used to decrease the rate of a chemical reaction is a(n) catalyst. enzyme. fuel. inhibitor. Answer: D - inhibitor

Section 4: Fire and Fire Safety Standard 8.5.c: Students know chemical reactions usually liberate heat or absorb heat.

Understanding Fire What are the three things necessary to maintain a fire? Three things necessary to start and maintain a fire are: fuel oxygen heat

Understanding Fire The fire triangle can be controlled in the grill. If any part of the fire triangle is missing, a fire will not continue.

Home Fire Safety If you know how to prevent fires in your home and what to do if a fire starts, you are better prepared to take action. The best form of fire safety is prevention.

Section 3 Quick Quiz In what way can a fire be brought under control? Add fuel. Add oxygen. Remove oxygen. Remove carbon dioxide. Answer: C – Remove oxygen

Section 3 Quick Quiz What is the best form of fire safety? a water hose an extinguisher the fire department fire prevention Answer: D – fire prevention

Section 3 Quick Quiz The best way to put out a small kitchen fire is to blow it out use a garden hose turn off the appliances cover it or use a home fire extinguisher Answer: D – cover it or use a home fire extinguisher