Chemical Reactions

Chemical Reactions 10.1 Reactions and Equations Evidence of Chemical Reactions.   The process of which the atoms of one or more substances are rearranged to form different substances is called a Chemical Reaction. Evidence of a Chemical Reaction 1. color change 2. formation of a solid (including smoke), liquid or gas 3. energy is released or absorbed (temp change), also gives off light, noise 4. odor

Representing Chemical Reactions Chemical Equations- are statements that chemists use to represent chemical reactions  They show: Reactants- the starting substances   Products- the substances formed during a reaction

Symbols Chemical equations show the direction in which a reaction takes place, so, an arrow is used rather than an equals sign. You read the arrow as “react to produce” or “yield”.

Word Equations Word equations describe the reactants and products of chemical reactions. Ex. reactant1 + reactant 2  product 1   iron(s) + chlorine(g)  iron(III) chloride(s) This equation is read: iron and chlorine react to produce iron(III)chloride

Skeleton Equations A skeleton equation uses chemical formulas rather than words to identify the reactants and the products. Ex: iron(s) + chlorine(g)  iron(III) chloride(s) Fe(s) + Cl2(g)  FeCl3 (s)

Writing Ionic Compound Formulas Review. 1. Write the symbols 2. Write the charges 3. Cross the charges from top to bottom. 4. Remove the charges 5. Simplify the numbers (ratios) and remove the ones. Reminder: treat polyatomic ions as one ion.

Balancing Chemical Equations. The law of conservation of matter states that, in a chemical change, matter is neither created nor destroyed.

Balancing Chemical Equations. Chemical equations must show that matter is conserved during a chemical reaction. Such an equation is called a balanced equation.

Balancing Chemical Equations.  To balance an equation you must find the correct coefficients for the chemical formulas in the skeletal equations. A coefficient in a chemical equation is the number written in front of a reactant or product.

Balancing Chemical Equations.  Coefficients are whole numbers and are not written if the value is 1. In a balanced equation, coefficient is the lowest whole-number ratio of the amounts of all the reactants and products.

Steps for Balancing Equations 1. Write the skeletal equation for the reaction. 2. Count the atoms of the elements in the reactants. 3. Count the elements in the products. 4. Change the coefficients to make the number of atoms of each element equal on both sides of the equation. 5. Write the coefficients in their lowest possible ratio. 6. Check your work.

Steps for Balancing Equations 1. Write the skeletal equation for the reaction.

Steps for Balancing Equations 2. Count the atoms of the elements in the reactants.

Steps for Balancing Equations 3. Count the elements in the products.

Steps for Balancing Equations 4. Change the coefficients to make the number of atoms of each element equal on both

Steps for Balancing Equations 5. Write the coefficients in their lowest possible ratio. Ratio is 1:1:2; so it is the lowest possible ratio

Steps for Balancing Equations 6. Check your work. Make sure the chemical formulas are written correctly. Check that the number of atoms is equal on both sides.

Recommended order of balancing 1. Metals 2. Non-metals 3. Polyatomic ions 4 Oxygen and hydrogen MgCl2 + Na2O  MgO + NaCl

Try to balance these equations!

Do Now In your packet: Write a skeletal equation of the following reactions and then balance.

FeCl3(aq) + 3NaOH  Fe(OH)3(s) + 3NaCl(aq) CS2(L) + 3O2(g)  CO2(g) + 2SO2(g) Zn(s) + H2SO4(aq)  H2(g) + ZnSO4(aq)

Classifying Chemical Reactions  Synthesis Reaction When two elements or substances react it is always a synthesis reaction. A + B  AB

Synthesis Reaction

Classifying Chemical Reactions    Combustion Reaction In combustion reactions, oxygen combines with a substance and releases energy in the form of heat and light. Ex  

Decomposition Reactions A decomposition reaction is one in which a single compound breaks down into two or more compounds or elements. AB  A + B

Decomposition Reactions AB  A + B Decomposition reactions often require an energy source such as heat or electricity, to occur.

Replacement Reactions  Single Replacement Reactions In a single-replacement reaction, the atoms of one element replace the atoms of another element in a compound. A + BX  AX + B

Replacement Reactions Single Replacement Reactions A + BX  AX + B

Replacement Reactions Single Replacement Reactions A + BX  AX + B

You can use the Activity Series Chart to predict if a single replacement reaction will occur. A specific metal can replace any metal listed below it. It cannot replace any metal listed above it.

Single Replacement Reactions

Replacement Reactions Double Replacement Reaction In a double replacement reaction ions are exchanges between two compounds.

Replacement Reactions

A solid produced during a chemical reaction is called a precipitate. A double replacement reaction will produce either a precipitate, a gas, or water. You can predict which ions will form a precipitate by using a solubility table.

Classifying Chemical Equations   __B__ 1. A + B  AB a. Decomposition Reaction __C__ 2. A + BX  B + AX b. Synthesis Reaction __D__ 3. AX + BY  AY + BX c. Single Replacement Reaction __E__ 4. CxHy + O2  CO2 + H2O d. Double Replacement __A__ 5. AB  A + B e. Combustion Reaction

Types of Reactions http://www. youtube. com/watch   Do Now Synthesis Reaction  1. CO2  C + O2 A + B  AB 2. CH4 + O2  CO2 + 2H2O Decomposition Reactions 3. NaCl + AgNO3  AgCl + NaNO3 AB  A + B 4. S + Cl2  SCl2 Combustion Reaction 5. Zn + 2HCl  ZnCl2 + H2 Replacement Reactions Single Replacement A + BX  AX + B Double replacement AX + BY  AY + BX

27. synthesis, combustion, decomposition, single replacement, double replacement. 28. Oxygen combines with a substance and releases energy in the form of heat and light. 29. In a single replacement reaction, atoms of one element replace atoms of another element in a compound. In a double replacement reaction two compounds dissolved in water exchange positive ions.

30. Double replacement reactions produce two different compounds, one being a solid precipitate, water or gas. 31. The reaction does occur because nickel is more reactive than gold. 32. A synthesis reaction will likely occur. Ba + F2  BaF2

Reactions in Aqueous Solutions An aqueous solution is substance dissolved in water. A substance dissolved in a solution is called a solute. The substance that dissolves a solute to form a solution is called a solvent. In an aqueous solution the solvent is water.

Reactions that Form Precipitates A precipitate is a solid produced in a chemical reaction in a solution. You can predict if a solid is formed in a double replacement reaction by using a solubility chart. Simply pick the compound that does not dissolve in water.

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