Chemical Reactions Applied Chemistry

Chemical Reaction Chemical reaction – The type of reaction in which the properties of the reactants are different from the products. Chemical reaction – The type of reaction in which the properties of the reactants are different from the products. Chemical Change – A change that produces new substances with new properties and compositions. Chemical Change – A change that produces new substances with new properties and compositions. Physical changes do NOT change the identity of a substance. Physical changes do NOT change the identity of a substance. Nuclear changes involve changes to the nucleus. Ex) fission and fusion Nuclear changes involve changes to the nucleus. Ex) fission and fusion

Signs of a chemical change Change in color Change in color Formation of a precipitate (cloudiness, solid formed from 2 solutions) Formation of a precipitate (cloudiness, solid formed from 2 solutions) Production of a gas (bubbles; fizzing) Production of a gas (bubbles; fizzing) Increase or decrease in temperature Increase or decrease in temperature Change or production of an odor Change or production of an odor

Chemical Equations A description of a chemical reaction using symbols instead of words. A description of a chemical reaction using symbols instead of words. Parts of a Chemical Equation: Parts of a Chemical Equation: A. Reactants B. Products C. Arrow D. Plus Sign

Parts of Chemical Equation A. Reactants CH 4 + O 2  H 2 O + CO 2 reactants products reactants products Written on the left side of the arrow Written on the left side of the arrow Starting material in a chemical reaction Starting material in a chemical reaction

Parts of Chemical Equation B. Products CH 4 + O 2  H 2 O + CO 2 reactants products reactants products Written on the right side of the arrow. Written on the right side of the arrow. Newly formed substances that are produced in a chemical reaction. Newly formed substances that are produced in a chemical reaction. Properties are different than those of the reactants. Properties are different than those of the reactants.

Parts of Chemical Equation C. Arrow CH 4 + O 2  H 2 O + CO 2 reactants products reactants products Yield sign Yield sign Means yields or produces Means yields or produces Separates the reactants from the products. Separates the reactants from the products.

Parts of Chemical Equation D. Plus sign CH 4 + O 2  H 2 O + CO 2 reactants products reactants products Used to separate reactants and to separate products Used to separate reactants and to separate products

Symbols for states H 2 (g) + O 2 (g)  H 2 O (l) KI (aq) + Pb(NO 3 ) 2 (aq)  PbI 2(s) + KNO 3(aq) Physical states of the reactants and products are in parenthesis beside the formula. g: gas g: gas l:liquid l:liquid s:solid s:solid aq: aqueous (dissolved in water) aq: aqueous (dissolved in water)

Example Reaction H 2 (g) + Cl 2 (g) → HCl (g) What are the reactants? What are the reactants? What are the products? What are the products? What is the physical state of all the substances? What is the physical state of all the substances? H 2 and Cl 2 HCl gas

Catalysts Catalysts are sometimes added to reactants to help speed up a chemical reaction. Catalysts are sometimes added to reactants to help speed up a chemical reaction. Catalysts are unchanged in a chemical reaction. They are neither reactants nor products. Catalysts are unchanged in a chemical reaction. They are neither reactants nor products. Catalysts are written above the yield sign. Catalysts are written above the yield sign.

Law of Conservation of Mass Mass is neither created nor destroyed in a chemical reaction, it can only change form. Mass is neither created nor destroyed in a chemical reaction, it can only change form. Mass of the reactants is the SAME as the mass of the products. Mass of the reactants is the SAME as the mass of the products. The number of each type of atom in the reactants must be equal to the number of atoms in the products. The number of each type of atom in the reactants must be equal to the number of atoms in the products. Since the number of atoms is the same, the mass will be the same on both sides of the reaction. Since the number of atoms is the same, the mass will be the same on both sides of the reaction. Also, the types of elements will be the same on each side. Also, the types of elements will be the same on each side.

Balancing Equations H 2 (g) + Cl 2 (g) → HCl (g) Reactant sideProduct side # of H atoms = 2# of H atoms = 1 # of Cl atoms = 2# of Cl atoms = 1 Does this equation have the same number of atoms of each element on both sides of the equation? Does this equation have the same number of atoms of each element on both sides of the equation? Therefore, it does not follow the Law of Conservation of Mass. Therefore, it does not follow the Law of Conservation of Mass. NO!!!

Balancing Equations (cont.) H 2 (g) + Cl 2 (g) → HCl (g) This equation is called a skeleton equation. This equation is called a skeleton equation. This equation must be balanced with coefficients (the number in front of a formula for a substance). This equation must be balanced with coefficients (the number in front of a formula for a substance).

a BALANCED Equation… H 2 (g) + Cl 2 (g) → 2HCl (g) Reactant sideProduct side # of H atoms = 2# of H atoms = 2 # of Cl atoms = 2# of Cl atoms = 2 A coefficient of 1(one) is understood and is not necessary in the balanced chemical equation.

Steps for balancing equations 1. Write the chemical formula for each reactant and product. 2. Indicate the state of each substance. 3. Use coefficients in front of the substance to balance the equation. The number of each atom should be the SAME on both sides of the equation. NOTE: NEVER CHANGE SUBSCRIPTS!!!

Balancing Examples 1. H 2 + Br 2 → 2HBr 2. 2Na + Cl 2 → 2NaCl 3. 4Na + O 2 → 2Na 2 O 4. Zn + 2HCl → ZnCl 2 + H Fe + 3O 2 → 2Fe 2 O 3

Balancing Examples 6. P 4 + 5O 2 → 2P 2 O 5 7. Al 2 O 3 + 3H 2 → 2Al + 3H 2 O 8. 2Ca + O 2 → 2CaO 9. 3Cl 2 + 2AlBr 3 → 3Br 2 + 2AlCl HgO → 2Hg + O 2

Synthesis Reactions Two or more reactants produce ONE product Two or more reactants produce ONE product A.K.A. Direct combination reactants A.K.A. Direct combination reactants Follows the pattern: A + B → AB Follows the pattern: A + B → AB **only ONE product** N 2 + 3H 2 → 2NH 3 2 reactants → 1 product

Synthesis Reaction

Combustion Reactions Chemical reaction involving oxygen (O 2 ) in which light and heat are produced. Heat is a useful product. Chemical reaction involving oxygen (O 2 ) in which light and heat are produced. Heat is a useful product. When fuels are burned in the presence of oxygen, water (H 2 O) and carbon dioxide (CO 2 ) are often produced. When fuels are burned in the presence of oxygen, water (H 2 O) and carbon dioxide (CO 2 ) are often produced. Follows the pattern: BC + A → BA + CA Follows the pattern: BC + A → BA + CA CH 4 (g) + 2O 2 (g) → CO 2 (g) + 2H 2 O (g) + heat

Combustion Reaction

Decomposition Reactions Opposite of synthesis reactions Opposite of synthesis reactions Substance breaks down into simpler substances. Substance breaks down into simpler substances. Chemists can cause decomposition, but decomposition can also be spontaneous. Chemists can cause decomposition, but decomposition can also be spontaneous. AB → A + B Only ONE reactant! 2H 2 O → 2H 2 + O 2 1 reactant → 2 products

Single Displacement (Replacement) Reactions Change in bonds. Change in bonds. One substance will replace, or bump out, another element in a compound. One substance will replace, or bump out, another element in a compound. A + BC → AC + B (2 reactants – element and compound 2 products – element and compound) Zn + H 2 SO 4 → ZnSO 4 + H 2

Double Displacement (Replacement) Reactions Both substances change partners Both substances change partners AB + CD → AD + CB 2KI (aq) + Pb(NO 3 ) 2 (aq)  2KNO 3 (aq) + PbI 2 (s) 2 reactants (both compounds) and 2 products (both compounds)

Synthesis Decomposition SR DR

Energy Changes in Reactions Exothermic Reactions Release heat into the surroundings Release heat into the surroundings Surroundings will get hotter. Surroundings will get hotter. Sometimes need heat to them started. Sometimes need heat to them started. A noticeable increase in temperature occurs. A noticeable increase in temperature occurs. Ex. Combustion & Burning Mg Ex. Combustion & Burning Mg

Energy Changes in Reactions Endothermic Reactions Absorb heat from the surroundings. Absorb heat from the surroundings. Surroundings will get cooler. Surroundings will get cooler. Need heat to keep them going. Need heat to keep them going. A noticeable decrease in temperature occurs. A noticeable decrease in temperature occurs. Ex. Photosynthesis and cold packs Ex. Photosynthesis and cold packs

The reactivity of a metal is based on its ability to replace another in a compound. The metal is oxidized. The reactivity of a metal is based on its ability to replace another in a compound. The metal is oxidized. If a single replacement reaction occurs, the metal that “cuts in” is MORE reactive than the one that was removed or replaced. If a single replacement reaction occurs, the metal that “cuts in” is MORE reactive than the one that was removed or replaced. An activity series of metals is a listing that ranks metals according to their reactivity. An activity series of metals is a listing that ranks metals according to their reactivity. The most active metal is at the TOP of the list The most active metal is at the TOP of the list The least active metal is at the BOTTOM of the list The least active metal is at the BOTTOM of the list Reactivity or Activity of Metals

The ACTIVITY SERIES is listed below : lithiumpotassiumbariumstrontiumcalciumsodiummagnesiumaluminummanganesezincironcadmiumcobaltnickeltinleadhydrogencoppersilvermercurygold The most active metal is LITHIUM The least active metal is GOLD Which is more active nickel or iron? IRON

Examples of the Activity of Metals Al + CuCl 2  Cu + AlCl 3 Al + CuCl 2  Cu + AlCl 3 Mg + HCl  H 2 + MgCl 2 Mg + HCl  H 2 + MgCl 2 Cu + HCl  No Reaction! Cu + HCl  No Reaction!

Treatment of Metals Metals are treated to protect from corrosion or to make the metals better suited for specific purposes, such as, improving strength or making them more light weight. Metals are treated to protect from corrosion or to make the metals better suited for specific purposes, such as, improving strength or making them more light weight. Types of Metal Treatments Types of Metal Treatments Galvanizing = coating with zinc (electroplating) Galvanizing = coating with zinc (electroplating) Painting = painting helps prevent corrosion Painting = painting helps prevent corrosion Making alloys = mixture of 2/more metals or a metal and a nonmetal. Making alloys = mixture of 2/more metals or a metal and a nonmetal.

Common Alloys Bronze Bronze Brass Brass Steel Steel Stainless steel Stainless steel Pewter Pewter Solder Solder copper + tin copper + zinc iron + carbon iron, carbon + chromium lead, tin + silver copper, tin + antimony