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Write & balance rxns

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This document introduces chemical reactions and the key concepts involved. It discusses signs of a chemical reaction, the law of conservation of mass, writing and balancing chemical equations, and describing coefficients and states of matter in equations. Specific examples are provided to illustrate writing the complete chemical equation for a reaction based on the substances involved, and using a step-by-step process to balance the atoms on each side of an equation.

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I. Intro to Reactions Chp 11: Chemical Reactions
A.Signs of a Chemical Reaction Evolution of heat and light Formation of a gas Formation of a precipitate Color change
B.Law of Conservation of Mass mass is neither created nor destroyed in a chemical reaction 4 H 2 O 4 H 2 O 4 g 32 g 36 g total mass stays the same atoms can only rearrange
C. Chemical Equations A+B C+D REACTANTS PRODUCTS
C. Chemical Equations
D. Writing Equations Identify the substances involved. Use symbols to show: 2H 2 ( g ) + O 2 ( g ) 2H 2 O( g ) How many? - coefficient Of what? - chemical formula In what state? - physical state Remember the diatomic elements.
D. Writing Equations Two atoms of aluminum react with three units of aqueous copper(II) chloride to produce three atoms of copper and two units of aqueous aluminum chloride. How many? Of what? In what state? Al 2 ( s ) + 3 CuCl 2 ( aq ) 3 Cu ( s ) + 2 AlCl 3 ( aq )
E. Describing Equations Describing Coefficients : individual atom = atom covalent substance = molecule ionic substance = unit 3 molecules of carbon dioxide 2 atoms of magnesium 4 units of magnesium oxide 3CO 2 2Mg 4MgO
E. Describing Equations to produce How many? Of what? In what state? Zn( s ) + 2HCl( aq ) ZnCl 2 ( aq ) + H 2 ( g ) One atom of solid zinc reacts with two molecules of aqueous hydrochloric acid one unit of aqueous zinc chloride and one molecule of hydrogen gas.
II. Balancing Equations Chp 11: Chemical Reactions
A. Balancing Steps 1. Write the unbalanced equation. 2. Count atoms on each side. 3. Add coefficients to make #s equal. Coefficient subscript = # of atoms 4. Reduce coefficients to lowest possible ratio, if necessary. 5. Double check atom balance!!!
B. Helpful Tips Balance one element at a time. Update ALL atom counts after adding a coefficient. If an element appears more than once per side, balance it last. Balance polyatomic ions as single units. 1 SO 4 instead of 1 S and 4 O
C. Balancing Example Aluminum and copper(II) chloride react to form copper and aluminum chloride. 1 1 1 1 2 3 2 3 6 3 3 3 2 2 2 6 Al + CuCl 2 Cu + AlCl 3 Al Cu Cl

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Write & balance rxns

  • 1. I. Intro to Reactions Chp 11: Chemical Reactions
  • 2. A.Signs of a Chemical Reaction Evolution of heat and light Formation of a gas Formation of a precipitate Color change
  • 3. B.Law of Conservation of Mass mass is neither created nor destroyed in a chemical reaction 4 H 2 O 4 H 2 O 4 g 32 g 36 g total mass stays the same atoms can only rearrange
  • 4. C. Chemical Equations A+B C+D REACTANTS PRODUCTS
  • 6. D. Writing Equations Identify the substances involved. Use symbols to show: 2H 2 ( g ) + O 2 ( g ) 2H 2 O( g ) How many? - coefficient Of what? - chemical formula In what state? - physical state Remember the diatomic elements.
  • 7. D. Writing Equations Two atoms of aluminum react with three units of aqueous copper(II) chloride to produce three atoms of copper and two units of aqueous aluminum chloride. How many? Of what? In what state? Al 2 ( s ) + 3 CuCl 2 ( aq ) 3 Cu ( s ) + 2 AlCl 3 ( aq )
  • 8. E. Describing Equations Describing Coefficients : individual atom = atom covalent substance = molecule ionic substance = unit 3 molecules of carbon dioxide 2 atoms of magnesium 4 units of magnesium oxide 3CO 2 2Mg 4MgO
  • 9. E. Describing Equations to produce How many? Of what? In what state? Zn( s ) + 2HCl( aq ) ZnCl 2 ( aq ) + H 2 ( g ) One atom of solid zinc reacts with two molecules of aqueous hydrochloric acid one unit of aqueous zinc chloride and one molecule of hydrogen gas.
  • 10. II. Balancing Equations Chp 11: Chemical Reactions
  • 11. A. Balancing Steps 1. Write the unbalanced equation. 2. Count atoms on each side. 3. Add coefficients to make #s equal. Coefficient subscript = # of atoms 4. Reduce coefficients to lowest possible ratio, if necessary. 5. Double check atom balance!!!
  • 12. B. Helpful Tips Balance one element at a time. Update ALL atom counts after adding a coefficient. If an element appears more than once per side, balance it last. Balance polyatomic ions as single units. 1 SO 4 instead of 1 S and 4 O
  • 13. C. Balancing Example Aluminum and copper(II) chloride react to form copper and aluminum chloride. 1 1 1 1 2 3 2 3 6 3 3 3 2 2 2 6 Al + CuCl 2 Cu + AlCl 3 Al Cu Cl