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Writing Chemical Equations Text Reference: Ch 7, Section 2

Writing Chemical Equations Text Reference: Ch 7, Section 2. Chemical Reactions. A chemical reaction is a process. What does this mean? Give some examples of processes Is baking a cake a process? Name some ingredients of baking a cake What is the product of this baking a cake process?

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Writing Chemical Equations Text Reference: Ch 7, Section 2

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  1. Writing Chemical EquationsText Reference: Ch 7, Section 2

  2. Chemical Reactions • A chemical reaction is a process. • What does this mean? • Give some examples of processes • Is baking a cake a process? • Name some ingredients of baking a cake • What is the product of this baking a cake process? • The cake – duh! • What symbol do we use to show processes? • 

  3. Chemical Reactions • In a chemical reaction, the  can be read as “produces” or “yields” • With a chem. Rx. (chemical reaction) something(s) new is produced from other chemical ingredients. • The arrow indicates the process of burning, combining, exploding, disintegrating…. • To the left of the arrow is what goes into the reaction: • Reactants, separated by + signs • On the right: ? • Products, also separated by + signs

  4. Chemical Reactions • Convert baking a cake into a chemical reaction • Flour(s) + water(l) + eggs(s) + milk(l), etc  cake(s) + good aroma filling the kitchen!(g) • Ingredients are reactants • Cake + aroma = products •  = heat (produces, yields) • You know a chemical reaction has occurred because you can’t reverse it.

  5. Old Prerequisites for Writing Chemical Equations(things you should/must already know) • Elements from periodic table • How to write ionic and covalent compound names • How to interpret word problems

  6. New Prerequisites for writing chemical equations • (l) = liquid state • (s) = solid state • (g) = gas • (aq) = aqueous (dissolved in water; solution) • The BrINClHOF’s • Guess what elements these are • bromine, • iodine, • nitrogen, • chlorine, • hydrogen, • oxygen, • fluorine

  7. New Prerequisites for writing chemical equations • The BrINClHOF’s • Always exist in pairs, when not combined with other elements • Gas at room temp. • Referred to by their normal chemical name even though they’re combined • ie. “chlorine” = Cl2(g) • “oxygen” = O2(g) • AKA: “HON and the halogens” • Or Hydrogen + 7

  8. Other Things Helpful to Know • When metals are just named (i.e., “lead”) this is simply the solid pure element (i.e., Pb(s)) • When things are “bubbled in” that means a gas form of that element is being added: • Ex: “hydrogen is bubbled into a solution of…” • Is written as: H2(g) + …  … • “Solutions” are aqueous. Ex: “ a solution of lead(II)chloride…” = • PbCl2(aq) • Acids are aqueous

  9. Rules for Writing Chem Equations • Figure out which are reactants and which are products. • Write chemical formulas for all substances, separated by the  • Add state of matter to each substance • Balance equation (to learn Friday)

  10. Writing Chem. Equation Examples • Zinc and aqueous lead(II)nitrate are combined in an aqueous solution to produce zinc nitrate and a lead precipitate. • zinc and lead(II)nitrate are reactants; zinc nitrate and lead are products • Zn + Pb(NO3)2  Zn(NO3)2 + Pb • Zn(s)+ Pb(NO3)2(aq) Zn(NO3)2(aq)+ Pb(s) • Balancing Friday

  11. Writing Chem. Equation examples • Carbon tetrachloride may be prepared by the reaction of natural gas, methane, and chlorine in the presence of ultraviolet light. Hydrochloric acid (HCl) is also a product of this reaction. • Carbon tetrachloride and hydrochloric acid are the products; methane and chlorine are the reactants • CH4 + Cl2  CCl4 + HCl • CH4(g) + Cl2(g)  CCl4(s) + HCl(aq) • To Balance Friday

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