Chemical PropertiesChanges What physical properties of a substance

Chemical Properties-Changes

• What physical properties of a substance are related to the potential for the substance to undergo physical change? – TIP If students have difficulty with this concept, begin by listing physical properties and ask students to think about the physical change that is associated with that property.

Answer • state of matter, because it relates to a substance changing states; melting point and boiling point, because they also relate to a substance changing states; solubility, because it relates to a substance dissolving and becoming part of a solution

LESSON INTRODUCTION Get Ready Before you begin, decide if you agree or disagree with each of these statements. As you view this presentation, see if you change your mind about any of the statements.

LESSON 4 Chemical Properties and Changes LESSON INTRODUCTION Get Ready What do you think? Before you begin, decide if you agree or disagree with each of these statements. As you view this presentation, see if you change your mind about any of the statements.

LESSON 4 Chemical Properties and Changes LESSON INTRODUCTION Get Ready Do you agree or disagree? • When wood burns, new materials form. • Temperature can affect the rate at which chemical changes occur.

LESSON 4 Chemical Properties and Changes LESSON INTRODUCTION Key Concepts/Essential Questions • What is a chemical property? • What are some signs of chemical change? • Why are chemical equations useful? • What are some factors that affect the rate of chemical reactions?

LESSON 4 Chemical Properties and Changes LESSON INTRODUCTION Vocabulary Watch out for these words! • chemical property • chemical change • concentration

About the Photo • This firefighter is extinguishing a burning car. The ability to burn is a chemical property. Some materials burn easily, while others do not. Some materials quickly turn to ash, while others take much longer to burn. But regardless of how quickly a material burns, it always undergoes a chemical change in the process.

• Why do you think metal is often used to make screens for fireplaces? – Most metal does not burn or melt at temperatures reached in fireplaces. • How has the metal in this car changed? How is it the same? – Its color, shape, and texture have changed. It is still metal.

LESSON 4 Chemical Properties and Changes LESSON INTRODUCTION A Burning Issue? Look at the photo at the beginning of the lesson. As this car burns, some materials change to ashes and gases. The metal might change form or state if the fire is hot enough, but it probably won’t burn. Why do fabric, leather, and paint burn? Why do many metals not burn? The properties of matter determine how matter behaves when it undergoes a change.

LESSON Brainpop LESSON INTRODUCTION http: //www. brainpop. com/science/matterandc hemistry/propertychanges/preview. weml

Teacher Demo

Lesson 4 notes • Lesson 4: Chemical Properties and Changes • A. Chemical Properties • 1. A(n) chemical property is a characteristic of matter that can be observed as it changes to a different type of matter. • 2. The ability of a fuel to burn is one example of a chemical property, and the ability of iron to rust is another example. • B. Comparing Properties • 1. All matter can be described by using its physical properties and its chemical properties.

Lesson 4 notes • 2. The difference in the types of properties is whether or not the matter changed identity while it was being observed. • C. Chemical Changes • 1. A(n) chemical change is a change in matter in which the substances that make upthe matter change into other substances that have new physical and chemical properties. • 2. New substances that are formed no longer have the same identity because they no longer have the same properties.

Lesson 4 notes • D. Signs of Chemical Change • 1. The formation of bubbles can indicate a chemical change. • 2. Energy is released during a fireworks explosion because a chemical change occurred. • 3. When fruit rots, changes in color and odor show that a chemical change occurred. • 4. These signs of chemical change only show that a(n) chemical change might have occurred; some of these signs also occur during physical changes. • 5. The only sure sign that a chemical change occurred is when new substances form.

Lesson 4 notes • E. Explaining Chemical Reactions • 1. Another name for a chemical change is a(n) chemical reaction. • 2. A chemical reaction occurs when atoms rearrange during a chemical change. • 3. A chemical reaction can be represented by a(n) chemical equation, which shows the chemical formula of each substance in the reaction.

Lesson 4 notes • a. A(n) arrow indicates that a reaction takes place. • b. The formulas to the left of the arrow in the equation represent the reactants, which are the substances that are present before the reaction began. • c. The formulas to the right of the arrow in the equation represent the products, which are the substances that are present after the reaction is complete.

Lesson 4 notes • 4. Chemical equations must be balanced, because mass is conserved during a chemical reaction. • a. When balancing a chemical equation, you cannot change the chemical formula of any reactant or product. • b. To balance the equation, numbers called coefficients are placed in front of the chemical formulas.

Lesson 4 notes • F. The Rate of Chemical Reactions • 1. Higher temperature usually increases rate of reaction because the particles move more quickly and collide harder. • 2. Concentration is the amount of substance in a certain volume. Reaction rate increases when concentration increases. • 3. Surface area affects reaction rate if at least one reactant is a solid. Reaction rate is faster if surface area is large.

Discussion Question • What can a baker do to slow down the chemical reaction that causes bread to mold? – He or she can reduce the temperature at which the bread is kept or increase the concentration of anything added to keep the bread fresh.

Chemical Properties-review • Substances are able to undergo a wide range of chemical changes. Knowing the chemical properties of a substance can be helpful if you are trying to cause a change or avoid an unwanted change. • What are some chemical properties of matter? – ability to burn, ability to rust, ability to rot

Chemical Changes-review • …focus on the atoms in the substances involved. As each substance undergoes a change, the atoms rearrange into different combinations. Chemical changes create new substances with their own physical properties. • How does rust form? – A chemical change occurs between iron and oxygen.

Chemical Changes-review • What is the difference between a physical change and a chemical change? – During a physical change, no new substance forms. During a chemical change, new substances form.

Signs of Chemical Change-review • what happens during a chemical change, it is necessary to describe each substance at the beginning and at the end of the change, and then determine what happened during the process. • For example, a fresh apple has a certain color and odor. But shortly after the apple is cut, a chemical change occurs as the apple reacts with oxygen. As a result, the color of the fruit darkens, and its odor changes. • study Figure 16, and compare the different signs.

Signs of Chemical Change-review • Does the formation of bubbles always indicate a chemical change? – No, because bubbles form when water boils, which is a physical change, not a chemical change. • What are signs of a chemical change? – formation of bubbles, energy change, change in color or odor • What signs show that a chemical change takes place when fireworks explode? – There is an energy change when light and thermal energy are released.

Explaining Chemical Reactions-review • A chemical change involves bond-breaking and bond-making. • What does it mean to say that atoms rearrange during a chemical change? – The same atoms are present before and after a chemical reaction, they are in different substances as products. • Why are chemical equations useful? – A chemical equation shows the chemical formula and number of units of each substance in the reaction.

The Rate of Chemical Reactions-review • Chemical changes involve particle collisions that might or might not result in a chemical reaction, depending on how fast the reactant particles are moving and how reactive they are. Temperature, concentration, surface area, and even orientation can affect how many collisions occur between reactants and the amount of force with which they collide. • study Figure 19. …. describe how the different factors affect the chemical reactions in each photo.

The Rate of Chemical Reactions-review • In general, how does an increase in temperature affect a chemical reaction? – In general, increasing thermal energy makes it possible for the particles in the substances to move faster and collide harder than at a lower temperature. This speeds up the chemical reaction.

The Rate of Chemical Reactions-review • List three factors that affect the rate of a chemical reaction. – Temperature, concentration, and the amount of surface area affect reaction rate.

LESSON 4 Chemical Properties and Changes LESSON WRAP-UP Lesson Review Do you agree or disagree? When wood burns, new materials form. Agree. When wood burns, new materials form, such as water and carbon dioxide.

LESSON 4 Chemical Properties and Changes LESSON WRAP-UP Lesson Review Do you agree or disagree? Temperature can affect the rate at which chemical changes occur. Agree. In general, increased temperature increases the rate of chemical change.

LESSON 4 Chemical Properties and Changes LESSON WRAP-UP Key Concept/Essential Question Review What is a chemical property? Chemical properties include ability to burn, acidity and ability to rust.

LESSON 4 Chemical Properties and Changes LESSON WRAP-UP Key Concept/Essential Question Review What are some signs of chemical change? Some signs that might indicate chemical changes are the formation of bubbles and a change in odor, color, or energy.

LESSON 4 Chemical Properties and Changes LESSON WRAP-UP Key Concept/Essential Question Review Why are chemical equations useful? Chemical equations are useful because they show what happens during a chemical reaction.

LESSON 4 Chemical Properties and Changes LESSON WRAP-UP Key Concept/Essential Question Review What are some factors that affect the rate of chemical reactions? Some factors that affect the rate of chemical reactions are temperature, concentration, and surface area.