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Chapter 9.1: Understanding Chemical Reactions
 

Chapter 9.1: Understanding Chemical Reactions

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Grade 8 Integrated Science Chapter 9 Lesson 1 on understanding chemical reactions. An introduction to reactants, products, and reading chemical equations.

Grade 8 Integrated Science Chapter 9 Lesson 1 on understanding chemical reactions. An introduction to reactants, products, and reading chemical equations.

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    Chapter 9.1: Understanding Chemical Reactions Chapter 9.1: Understanding Chemical Reactions Document Transcript

    • Chapter 9 Lesson 1: Understanding Chemical Reactions – p 300-310 – page 1 Vocabulary • Chemical reaction (301) – a process in which atoms of one or more substances rearrange to form one or more new substances • Chemical equation (304) – a description of a reaction using element symbols and chemical formulas • Reactant (305) – the starting substances in a chemical reaction • Product (305) – the substances produced by the chemical reaction • Law of Conservation of mass (306) – The law of conservation of mass states that the total mass of the reactants before a chemical reaction is the same as the total mass of the products after the chemical reaction • Coefficient (308) – a number placed in front of an element symbol or chemical formula in an equation Changes in Matter Physical Changes Chemical Changes • • • • • • • What are chemical changes called? ______________________________________________ • A chemical reaction is a process in which atoms of one or more substances rearrange to form one or more new substances. Signs of a Chemical Reaction • Changes in the physical properties of color, state of matter, and odor are all signs that a ___________________ might have occurred • A change is ____________ is another sign. Changes in Physical Properties Changes in Energy       What happens in a chemical reaction?
    • Chapter 9 Lesson 1: Understanding Chemical Reactions – p 300-310 – page 2 • Atoms rearrange to form new substances – There are 2 types of substances: ___________________ and ______________________ – Substances have a fixed ___________________________ of atoms – A drop of water each water molecule will have one oxygen atom bonded to two hydrogen atoms – If this arrangement changes the substance is no longer water and a __________________ substance has formed – The new substance will have ____________________ chemical and physical properties – This is what happens during a chemical reaction • Bonds break and bonds form – Atoms rearrange when chemical _____________________ between the atoms break – Particles are moving in all substances, even in _________________ – These particles ___________________ , or run into one another. – If particles collide with enough energy, the bonds between the atoms can_____________, separate, rearrange, and ______________ new bonds. Chemical Equations • A chemical _____________________ is a description of a reaction using element symbols and chemical formulas • Element symbols represent _________________________ • Chemical formulas represent ________________________ Elemental Symbols • Each element can exist as just one atom – C = carbon Cu = Copper • _______________ elements exist in nature as diatomic molecules – two atoms of the same element bonded together. – This is shown by a _________________________. – H2 = hydrogen O2 = oxygen Chemical Formulas • A chemical formulas uses elements’ symbols and subscripts to describe the number of atoms in a compound • If an element does not have a subscript, the compound contains only _____ atom of that element Writing Chemical Equations • A chemical equation included both the substances that react and the substances that are formed in a chemical equation.
    • • • • • Chapter 9 Lesson 1: Understanding Chemical Reactions – p 300-310 – page 3 The starting substances in a chemical reaction are the __________________________ The substances produced by the chemical reaction are _________________________ The arrow shows the direction of the reaction Reactants are written _____________of the arrow and products are written to the _________ Balanced: 2Na + Cl2 => 2NaCl Conservation of Mass • French chemist Antoine Lavoisier found that the total mass of the reactants _____________ equaled the total mass of the products. • This is the law of conservation of mass, which states that the ___________________________________________ before the reaction must equal the ___________________________________________ after the chemical equation. Atoms are conserved • Mass is conserved because __________________ are conserved • Bonds break and new bonds form during a chemical reaction • However, atoms are neither______________ nor _______________________ Balance the equations • An equation is written so that the number of atoms of each element is the_______________, or balanced, on each side of the arrow <= IMPORTANT! • Add________________________! • A coefficient is a number placed in ________________of an element symbol or chemical formula in an equation. • ______________ coefficients can be changed when balancing an equation. • Do not change subscripts!!! Changing subscripts changes the identities of the substances that are in the reaction. Coefficients Reactants Elements Products H Reactants O Balancing a Chemical Equation • Write the unbalanced equation. • Count atom of each element in the reactants and in the products. • Add coefficients to balance the atoms. • Write the balanced chemical equation. Products
    • Chapter 9 Lesson 1: Understanding Chemical Reactions – p 300-310 – page 4 Balance •____ N2 + ____ H2 → ____ NH3 •____ Al + ____ HCl → ____ AlCl3 + ____ H2 (g) Lighting a Candle • Lab