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Understanding Chemical Reactions: Reactants, Products, and the Conservation of Matter

This lesson explores the fundamentals of chemical reactions, including identifying reactants and products, the conservation of mass, and how chemical changes are expressed through equations. We differentiate between chemical reactions and nuclear reactions, emphasizing the role of electrons and nuclei. Through engaging examples like burning paper and baking soda reactions, we illustrate the law of conservation of mass, demonstrating that matter is neither created nor destroyed. Students will practice writing chemical equations, identifying coefficients, and understanding the states of matter involved.

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Understanding Chemical Reactions: Reactants, Products, and the Conservation of Matter

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  1. 3/15/12 – Bell ringer • Water freezing or boiling is not chemical reaction. Why? • Hold on to 4 bell ringers as we will turn them in at the end of notes

  2. Chapter 23 – Chemical Reactions 23.1 – Chemical Changes

  3. Objectives • 1. Identify the reactants and products in a chemical reaction. • 2. Determine how a chemical reaction satisfies the law of the conservation of matter. • 3. Determine how chemists express chemical changes using equations

  4. Chemical Reaction • A change in which one or more substances are converted to new substances • Reactants – the substances that react • Products – the new substances produced

  5. Different Reactions • Chemical reactions – use the ELECTRONS to form new substances • Nuclear reactions - use the NUCLEUS to form new substances • What does a chemical reaction look like?

  6. Chemistry Kitchen

  7. Chemistry Kitchen REACTANTS PRODUCTS

  8. Think about it… • If you burned a piece of paper, you end up with a pile of ashes. • Once burned, is there… • More mass? • Same mass? • Less mass? • Why?

  9. Conservation of Mass • Law that states in a chemical reaction, matter is not created or destroyed • Antoine Lavoisier experimented with mercury (II) oxide and heat • He found mass of products (liquid mercury and oxygen gas) equaled mass of reactants

  10. Chemical Equation • Uses chemical formulas and symbols to describe a chemical reaction and the product(s) it produces • Chemical formula expresses the relationship between elements in the compound and molecules they make up

  11. Chemical Equation Reactants (left) → Products (right) Arrow means “yields” SnO2(s) + 2 H2(g) → Sn(s) + 2 H2O(g) CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(g)

  12. Coefficients • Numbers which represent the number of units of each substance in a reaction • Knowing coefficients of chemical reactions allows chemists to use the correct amount of reactants to predict the amount of products (law of conservation applies)

  13. Example

  14. Writing equations • Subscripts = Numbers which represent the number of atoms in a molecule of a particular element • Symbols used to show state of reactants • (s) solids • (aq) aqueous • (l) liquid • (g) gas

  15. Volcano with a Twist • Reactants? • Products?

  16. Equation: NaHCO3 ( ) + CH3COOH ( )  CH3COO-Na+( ) + H2O ( ) + CO2( ) • States? • Conservation?

  17. Exit slip on BR paper • SnO2(s) + 2 H2(g) → Sn(s) + 2 H2O(g) • What are the reactants? • What are the products? • How is matter conserved/equalled out? • What changed? • (Compounds and States)

  18. In-class Assignment/Homework • 23.1 WKT

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