Chapter 6 Chemical Reactions 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 6 Chemical Reactions 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 6 Chemical Reactions 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 6 Chemical Reactions 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 6 Chemical Reactions 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 6 Chemical Reactions Chapter Preview Questions 3. Fe, which stands for iron, is a a. chemical symbol. b. chemical equation. c. atomic number. d. name.

Chapter 6 Chemical Reactions Chapter Preview Questions 3. Fe, which stands for iron, is a a. chemical symbol. b. chemical equation. c. atomic number. d. name.

Chapter 6 Chemical Reactions 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 6 Chemical Reactions 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 6 Chemical Reactions Section 1: Observing Chemical Change How can changes in matter be described? How can you tell when a chemical reaction occurs?

Chapter 6 Chemical Reactions Properties and Changes in Matter Matter can undergo both physical change and chemical change.

Chapter 6 Chemical Reactions Properties and Changes in Matter Chemical changes occur when bonds break and new bonds form.

Chapter 6 Chemical Reactions 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.

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

Chapter 6 Chemical Reactions Energy in Chemical Changes About 20ºC Calculating: How many degrees did the temperature drop between 2 minutes and 5 minutes?

Chapter 6 Chemical Reactions Energy in Chemical Changes The reaction was endothermic, because it absorbed thermal energy from the reaction mixture, causing the temperature to drop. Interpreting Data: Is the reaction endothermic or exothermic? Explain.

Chapter 6 Chemical Reactions Energy in Chemical Changes The reaction stopped at about 2ºC. You can tell because that is the lowest temperature reached. Inferring: At what temperature did the reaction stop? How can you tell?

Chapter 6 Chemical Reactions Energy in Chemical Changes If the temperature increased instead, the reaction would be exothermic, because an exothermic reaction is one in which energy is released. 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.

Chapter 6 Chemical Reactions Section 2: Describing Chemical Reactions What information does a chemical equation contain? How is matter conserved during a chemical reaction? What must a balanced chemical equation show? What are three types of chemical reactions?

Chapter 6 Chemical Reactions Describing Chemical Reactions Cellular phone messages use symbols and abbreviations to express ideas in shorter form. Similarly, chemists often use chemical equations in place of words.

Chapter 6 Chemical Reactions Chemical Formulas The formula of a compound identifies the elements in the compound and the ratios in which their atoms are present.

Chapter 6 Chemical Reactions What Are Chemical Equations? Chemical equations use chemical formulas and other symbols instead of words to summarize a reaction.

Chapter 6 Chemical Reactions 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.

Chapter 6 Chemical Reactions 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.

Chapter 6 Chemical Reactions Balancing Chemical Equations Magnesium (Mg) reacts with oxygen gas (O 2 ), 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.

Chapter 6 Chemical Reactions Balancing Chemical Equations Balancing Chemical Equations: Balance the equation for the reaction of sodium metal (Na) with oxygen gas (O 2 ), forming sodium oxide (Na 2 O).

Chapter 6 Chemical Reactions Balancing Chemical Equations Balancing Chemical Equations: Balance the equation for the reaction of tin (Sn) with chlorine gas (Cl 2 ), forming tin chloride (SnCl 2 ).

Chapter 6 Chemical Reactions Classifying Chemical Reactions Many chemical reactions can be classified in one of three categories: synthesis, decomposition, or replacement.

Chapter 6 Chemical Reactions Section 3: Controlling Chemical Reactions How is activation energy related to chemical reactions? What factors affect the rate of a chemical reaction?

Chapter 6 Chemical Reactions Energy and Reactions All chemical reactions require a certain amount of activation energy to get things started.

Chapter 6 Chemical Reactions Energy and Reactions Both exothermic and endothermic reactions need energy to get started.

 When concentrations are increased, more molecules are available to collide, and therefore collisions occur more frequently.  Higher concentration  higher reaction rate.

 Greater surface area allows particles to collide with many more particles per unit of time.  For the same mass, many small particles have more surface area than one large particle.  Reaction rate increases with increasing surface area.

 Increasing temperature generally increases reaction rate.  Increasing temperature increases the kinetic energy of the particles.  Reacting particles collide more frequently at higher temperatures.

 A catalyst is a substance that increases the rate of a chemical reaction without being consumed in the reaction.catalyst  An inhibitor is a substance that slows or prevents a reaction.inhibitor

Chapter 6 Chemical Reactions 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.

Chapter 6 Chemical Reactions Section 4: Fire and Fire Safety What are the three things necessary to maintain a fire? Why should you know about the causes of fire and how to prevent a fire?

Chapter 6 Chemical Reactions Understanding Fire Three things necessary to start and maintain a fire are fuel, oxygen, and heat.

Chapter 6 Chemical Reactions 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.

Chapter 6 Chemical Reactions 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.