2Chemical 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 Reaction1. color change2. formation of a solid (including smoke), liquid or gas3. energy is released or absorbed (temp change), also gives off light, noise4. odor
3Representing Chemical Reactions Chemical Equations- are statements that chemists use to represent chemical reactions They show:Reactants- the starting substancesProducts- the substances formed during a reaction
4SymbolsChemical 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”.
5Word EquationsWord equations describe the reactants and products of chemical reactions.Ex. reactant1 + reactant 2 product 1iron(s) + chlorine(g) iron(III) chloride(s)This equation is read: iron and chlorine react to produce iron(III)chloride
6Skeleton EquationsA 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)
9Writing Ionic Compound Formulas Review.1. Write the symbols2. Write the charges3. Cross the charges from top to bottom.4. Remove the charges5. Simplify the numbers (ratios) and remove the ones.Reminder: treat polyatomic ions as one ion.
10Balancing Chemical Equations. The law of conservation of matter states that, in a chemical change, matter is neither created nor destroyed.
11Balancing Chemical Equations. Chemical equations must show that matter is conserved during a chemical reaction. Such an equation is called a balanced equation.
12Balancing 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.
13Balancing 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.
14Steps 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 bothsides of the equation.5. Write the coefficients in their lowest possible ratio.6. Check your work.
15Steps for Balancing Equations 1. Write the skeletal equation for the reaction.
16Steps for Balancing Equations 2. Count the atoms of the elements in the reactants.
17Steps for Balancing Equations 3. Count the elements in the products.
18Steps for Balancing Equations 4. Change the coefficients to make the number of atoms of each element equal on both
19Steps for Balancing Equations 5. Write the coefficients in their lowest possible ratio.Ratio is 1:1:2; so it is the lowest possible ratio
20Steps 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.
21Recommended order of balancing 1. Metals2. Non-metals3. Polyatomic ions4 Oxygen and hydrogenMgCl2 + Na2O MgO + NaCl
44A 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.
46Classifying 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 ReplacementReaction__E__ 4. CxHy + O2 CO2 + H2O d. Double Replacement__A__ 5. AB A + B e. Combustion Reaction
47Types of Reactions http://www. youtube. com/watch Do NowSynthesis Reaction CO2 C + O2A + B AB CH4 + O2 CO H2ODecomposition Reactions NaCl + AgNO3 AgCl + NaNO3AB A + B S + Cl2 SCl2Combustion Reaction Zn + 2HCl ZnCl2 + H2Replacement ReactionsSingle ReplacementA + BX AX + BDouble replacementAX + BY AY + BX
5027. 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.
5130. 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
52Reactions 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.
53Reactions 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.