chemical rxn

Unit D Chapter 3Chemical ReactionsBy Jerry Mullins : 

Unit D Chapter 3Chemical ReactionsBy Jerry Mullins

Principle 2 : 

Principle 2 Matter Changes form and moves from place to place

Sections 3.1 Chemical reactions alter arrangements of atoms : 

Sections 3.1 Chemical reactions alter arrangements of atoms Atoms interact in chemical reactions Chemical reactions can be classified The rates of chemical reactions can vary

Section 3.1 Objective : 

Section 3.1 Objective The Student will: Define Key vocabulary Recognize evidence of chemical changes and describe how these changes occur Identify three types of chemical reactions Describe how the rate of a chemical reaction can be changed Infer through an experiment how the rate of a reaction can be changed by physically changing the reactants

Warm-Up : 

Warm-Up Transparency 20 overhead Draw a diagram showing a sodium atom, a chlorine atom, and the two of them bonded together as sodium chloride. How do sodium and chlorine bond to each other in this compound?

Vocabulary : 

Vocabulary Chemical reaction Physical change Chemical change Reactant Product Precipitate Synthesis Decomposition Combustions Catalyst

Explore Lab : 

Explore Lab “Chemical Changes” Question: How can you identify a chemical change? Material: Vinegar * clear bowl *plastic spoon *table salt 20 pennies *large iron nail Procedure: Pour about 3cm (1”) of vinegar into the bowl. Add a spoonful of salt. Stir until the salt dissolves Put the pennies into the bowl. Wait two minutes, and then put the nail into the bowl Observe the nail after 5 minutes and record your observations What do you think?: What did you see on the nail? Where do you think it came from? Did a new substance form? What evidence supports your conclusion?

Chemical Reaction : 

Chemical Reaction Chemical reaction (rxn): produces new substances by changing the way it which atoms are arranged Most chemical reactions take place when particles of reactants collide with enough force to react. Reactions can occur at different “rates” Bonds between atoms are broken and new bonds form between different atoms This breaking and forming takes place when particles of the original material collide with one another After a rxn the new arrangements of atoms form different substances

Physical changes : 

Physical changes Physical Changes: A change in the state of a substance; the substance may have some different properties afterwards, but it is still the same substance. The rate at which atoms or molecules in a substance move determines its physical state Atoms are in constant motion

Solid Physical State : 

Solid Physical State Solid Molecules tightly linked together in a definite shape Vibrate in place Fixed volume and shape

Liquid Physical State : 

Liquid Physical State Liquids Molecules not as tightly linked as a solid Maintain fixed volume Able to flow and conform to shape of container

Gas Physical State : 

Gas Physical State Gas Molecules have little or no attraction to each other Fill the volume of the occupied container Move most rapidly To cause a substance to change state, thermal energy must be added to or removed from a substance

More on Physical Changes : 

More on Physical Changes Substances can undergo different kinds of physical changes Sugar dissolves in water buy still tastes sweet because the molecules that make up sugar do not change when it dissolves The pressure of helium changes when it is pumped fro a high pressure tank into a balloon, but the gas still remains helium

Chemical Changes : 

Chemical Changes When the original material is changed into a different substance via a chemical reactions Electrolysis of water: Water molecules can be broken down into hydrogen and oxygen molecules by this chemical reaction of “electrolysis” that is , when electrical current is passed through liquid water it changes the water into two gases. Which then recombine into hydrogen molecules (H2) and oxygen molecules (O2) H2 and O2 is used as rocket fuel for the space shuttle. During liftoff. Liquid H2 and O2 are combined in a reaction opposite of electrolysis. The rxn produces water and a large amount of energy that pushes the shuttle into orbit

What is needed for a chemical reaction to take place? : 

What is needed for a chemical reaction to take place? Reactants Are the substances present at the beginning of a chemical reaction Burning of natural gas: Methane (CH4) and oxygen (O2) are the reactants in the chemical reactions Products: Are the substances formed by a chemical reaction Burning of natural gas: Carbon dioxide (CO2) and water (H2O) are the products formed by the reactions Reactants and Products can be elements or compounds depending on the reaction taking place

What is taking place in a chemical reactions? : 

What is taking place in a chemical reactions? Bonds between atoms in the reactants are broken and new bonds are formed in the products. When natural gas is burned, bonds between carbon and hydrogen atoms in methane are broken as are the bonds between the oxygen atoms in oxygen molecules.

Better understanding of chemical reactions : 

Better understanding of chemical reactions Reactants are shown on the left side of the arrow. Products are shown on the right side of the arrow The arrow indicates the actual reactions taking place The number of each kind of atom must be the same on either side of the arrow Bonds are broken Elements rearranged New compounds formed

How do you know when a reactions has occurred? : 

How do you know when a reactions has occurred? Some are easy to observe—others are not easy to see but can be detected in other ways Color change When gray iron rusts the product is brown Formation of a precipitate A solid product may form when chemical in two liquids react (seashells are formed this way when a sea creature releases a liquid that reacts with seawater Formation of a gas Antacid pill are mixed with excess stomach acid Temperature change Most rxns involve a temp change, sometimes this can be inferred from simple observation of a flame, (burning of metal magnesium). Others you do not readily see such as concrete before it hardens, if you touch it you may notice a warm sensation.

Classifying chemical reactions : 

Classifying chemical reactions First, all reactions form new products but the ways in which products are made can differ. Synthesis: Decomposition: Combustions:

Synthesis Reactions : 

Synthesis Reactions A new compound is formed by the combinations of simpler reactions (making a substance from simpler substances Nitrogen dioxide a component of smog forms when nitrogen and oxygen combine in the air

Decomposition Reactions : 

Decomposition Reactions A reaction breaks down into simpler products which could be elements or other compounds (separations into parts) Decomposition reactions can be though of as being a reverse of synthesis reactions Water decomposed into its elements—hydrogen and oxygen

Combustion Reactions : 

Combustion Reactions One reactant is always oxygen and another reactant often contains carbon and hydrogen. The carbon and hydrogen atoms combine with oxygen producing carbon dioxide and water (a process of burning with oxygen) The burning of methane is a combustion reactions

“RATES” of chemical reactions vary : 

“RATES” of chemical reactions vary Rates of chemical reactions can vary greatly Striking a match causes a very quick chemical reactions were as Rusting of an iron nail may take several months However, “RATE” of reactions can be altered/changed via three possible physical factors and one chemical factor: Concentration (physical) Surface area (physical) Temperature (physical) Catalyst (chemical)

Concentration Rates : 

Concentration Rates Is a measurement of the number of particles present in a certain volume High concentration of reactant means that there is a large number of particles that can collide and react

Surface Area Rate : 

Surface Area Rate Breaking a large piece of material into smaller parts increases the surface area of the material. All of the inner materials has no surface when it is inside a larger piece. Each time the large piece is broken the more surfaces are exposed. The amount of material does not change but breaking it into smaller parts increases its surface area Increasing the surface area therefore increases the rate of change. Example ice cube verse crushed ice

Temperature Rate : 

Temperature Rate Rate of reaction increased by making the particles move faster. Resulting in more collisions per time, as well as, per force Most common way to make particles move faster is to add energy to the reactant which in turn increases the temperature.

Catalysts rates : 

Catalysts rates Rate of a reactions can be changed by adding a catalyst. A substance that increases the rate of chemical reaction but is not itself consumed in the reaction very important in many industrial and biological reactions In living things a catalysts is termed enzymes and are needed for life without them many reactions would not take place

Sections 3.2 The masses of reactants and products are equal : 

Sections 3.2 The masses of reactants and products are equal Careful observations led to the discovery of the conservation of mass Chemical reactions can be described by chemical equations Chemical equations must be balanced

Section 3.2 Objective : 

Section 3.2 Objective The Student will: Define Key vocabulary; Explain why total mass does not change in a chemical reaction; Recognize how a chemical equation represents a chemical reaction; Outline how to balance a simple chemical equations; and Measure in an experiment the mass of reactants and products in a chemical reaction.

Warm-Up : 

Warm-Up Transparency 20 overhead Decide if these statements are true. If not, correct them.

Vocabulary : 

Vocabulary Law of conservation of mass coefficient

Investigative Lab : 

Investigative Lab “Conservation of Mass” Question: Why is it important to measure the masses of reactants and products? Material: Teaspoon * baking powder * funnel *Balloon * vinegar *plastic bottle Balance Procedure: Measure 2 tsp of baking soda. Use a funnel to put the baking soda in a balloon Pour 2 tsp of vinegar into the plastic bottle Secure the balloon over the mouth of the bottle with the balloon hanging to the side of the bottle. Find and record the mass of the experimental setup Lift the balloon so that the baking soda drops into the bottle observe for 5 minutes, and then find and record the mass of the setup again What do you think?: Did the mass of the experimental setup change? How did your observations demonstrate the conservations of mass?

Conservation of Mass : 

Conservation of Mass French Chemist in 1780’s showed that matter can never be created or destroyed in a chemical reaction He showed that reactions that seem to gain mass or lose mass actually involve reactions with gases in the air. These gases could not be seen but their masses could be measured “ in a chemical reaction atoms are neither created nor destroyed. All atoms present in the reactants are also present in the products”

Understanding Chemical Equations : 

Understanding Chemical Equations Chemical Equations: represent how atoms are rearranged in a chemical reaction. The atoms in the reactants are shown on the left side of the equations The atoms in the products are shown on the right side of the equations Because atoms are rearranged and not created or destroyed, the number of atoms of each different element must be the same on each side of the equations

What you need to know! : 

What you need to know! In order to write a chemical equation the information that you need to know is: The reactants and products in the reaction The atomic symbols and chemical formulas of the reactants and products in the reactions The directions of the reactions Remember the subscript (if any) indicated the number of atoms of an element in a molecule

Equations MUST be balanced : 

Equations MUST be balanced Remember rxns must follow the law of conservation of mass The same number of atoms must appear on both sides of the equation in order to be balanced Simply writing down the chemical formulas of reactants and products does not always result in equal numbers of atoms You have to balance the equation to make the number of atoms equal on each side of an equations

How to balance an equations : 

How to balance an equations Combustion of natural gas (mostly methane) the reactants are _______ and _______. The product are _______ and ______. Remember oxygen is always a reactant in a combustion reaction. However, what is wrong with the below equations? Is it balance?

Is it or is it not balanced? : 

Is it or is it not balanced? First count the atoms on each side of the equation and they must match up. One C on reactant and one C on Product (balanced) 4 H on reactant however, only two on Product (unbalanced) 2 O on reactant however, three O on the Product (unbalanced)

Lets balance the equation! : 

Lets balance the equation! We can balance the equation by changing the amounts of reactants or products.

Next step to balancing : 

Next step to balancing Lets balance H first, by adding another H2O to the Product side. Now the C and H are balanced

Final step in balancing : 

Final step in balancing There are now two oxygen atoms needed. So add an oxygen molecule to the reactant side. The equation is now balanced on both sides. Great Job!

Put it all together : 

Put it all together The balanced equation for the combustion of methane: one molecule of CH4 reacts with two molecules of O2 to produce one molecule of CO2 and two molecules of H2O The proper way to write out this equation. Pay attention to the subscript and coefficients

Remember what is a coefficient and subscript!!! : 

Remember what is a coefficient and subscript!!! Coefficient: the numbers in front of the chemical formulas. They indicate how many MOLECULES take part in the reaction If there is only one coefficient no number is written Subscript: the number after the chemical symbol to indicate how many individual ATOMS take part in the reaction

Rule to follow when dealing with both coefficient and subscript in the same formula : 

Rule to follow when dealing with both coefficient and subscript in the same formula Chemical formulas can have both coefficients and subscripts Multiple the two numbers together to find the number of atoms involved in the reactions Example: 2 H2O contain 2 * 2 = 4 hydrogen atoms and 2 * 1 = 2 Oxygen atoms ONLY!!! The coefficient can be changed in order to balance a chemical equation. Subscripts are part of the chemical formula for the reactants or products and CANNOT be changed to balance an equation If you change the subscript you will change the substance in the formula Practice with TE/PE 83

Lets Balance Some Equations : 

Lets Balance Some Equations Instructions: who can balance the equations http://www.wfu.edu/~ylwong/balanceeq/balanceq.html

Rags to Riches Game on Balancing Equations : 

Rags to Riches Game on Balancing Equations Instructions: who can balance the equations and earn points for your group? http://www.quia.com/rr/100887.html

Lets Balance Some More EquationsQuiz : 

Lets Balance Some More EquationsQuiz Instructions: who can balance the equations http://funbasedlearning.com/chemistry/chembalancer/default.htm

Sections 3.3 Chemical reactions involve energy changes : 

Sections 3.3 Chemical reactions involve energy changes Chemical reactions release or absorb energy; Exothermic reactions release energy; Endothermic reactions absorb energy. Exothermic and endothermic reactions work together to supply energy

Section 3.2 Objective : 

Section 3.2 Objective The Student will: Define Key vocabulary; Describe how energy changes in a chemical reaction; Explain how some chemical reactions release energy; and Explain how some chemical reactions absorb energy.

Warm-Up : 

Warm-Up Transparency 21 overhead Balance the following equations on the overhead

Vocabulary : 

Vocabulary Bond energy Exothermic reaction Endothermic reaction Photosynthesis

Explore Lab : 

Explore Lab “Energy Changes” Question: How can you identify a transfer of energy? Material: Graduated cylinder * hot tap water * plastic cup *thermometer Stopwatch *plastic spoon *Epsom salt Procedure: Pour 50 ml of hot tap water into the cup and place the thermometer in the cup Wait 30 seconds. Then record the temperature of the water Measure 5 tsp of Epsom salt. Add the Epsom salts to the beaker and immediately record the temperature while stirring the contents of the cup Continue to record the temperature every 30 seconds for 2 minutes What do you think?: What happened to the temperature after you added the Epsom salts? What do you think caused this change to occur

Overview : 

Overview Chemical reactions involve breaking bonds in reactants and forming new bonds in products Breaking bonds require ENERGY; and Forming bonds release ENERGY

Bond Energy : 

Bond Energy Energy associated with bonds This bond energy is different between bonds of various atoms Reactant molecules need Energy to break their bonds Product molecules release Energy when bonds are formed By adding up the bond energies in the reactant and products one can determine if energy will be released or absorbed

Exothermic Reactions : 

Exothermic Reactions If more energy is released when the products form than is needed to break the bonds in the reactants, then the energy is released during the reaction Energy is released from the reactions “exo” out

Endothermic Reactions release energy : 

Endothermic Reactions release energy If more energy is required to break the bonds in the reactants than is released when the products formed, then energy must be added to the reaction Energy is absorb from the reaction Each lab group complete a poster on TE/PE p88 Exothermic Reactions

Examples of energy : 

Examples of energy Endo- and exothermic energy changes can also be observed in different physical changes such as dissolving or changing physical states Liquid to a solid = release of energy (exothermic) Solid to a liquid = absorbs energy (endothermic) White clouds from shuttle liftoff is exothermic 2H2 + O2  2 H2O

More on exothermic reactions : 

More on exothermic reactions Often produce increase in temperature Bond energy of the reactants are less than the bond energies in the products. Therefore less energy is needed to break the bonds in the reactants (Reactants < Product) The energy difference between reactants and products is often released as HEAT Some reactions are highly exothermic known as thermite reactions (welders) Powdered aluminum metal with iron oxide 2 Al + Fe2O3  Al2O3 + 2 Fe This reactions releases enough heat to melt the iron that is produced Used to weld iron rails together.

More on exothermic reactions : 

More on exothermic reactions Other types of exothermic reactions: All common combustion reactions Some chemical rxns release excess energy as light instead of heat Glow sticks One of the reactants is a solution of hydrogen peroxide, contained in a glass container, the rest of the stick is filled with a second chemical and a brightly colored dye Also occur in living things Fireflies, fish, squid, jellyfish, and shrimp Due to rxn that takes place between oxygen and a chemical called luciferin Bombardier beetle use exothermic rxn as a defense

Endothermic reactions absorb energy! : 

Endothermic reactions absorb energy! Often produce a decrease in temperature The bond energies of the reactants are greater than the bond energies of the product (reactants > product) All endothermic reactions absorb energy however, they do not all absorb energy as heat Decomposition of water via electrolysis

Most important endothermic reaction on earth : 

Most important endothermic reaction on earth Photosynthesis 6CO2 + 6 H2O  C6H12O6 + 6O2 Photosynthesis does not absorb energy as heat. Instead plants absorb energy from sunlight to turn carbon dioxide and water into oxygen and glucose. The energy is stored in the glucose molecule and used later for energy when needed.

Endo and exothermic working together to supply energy : 

Endo and exothermic working together to supply energy Exothermic Rxn Reactants  Product + Energy Endothermic Rxn Reactants + Energy  Product If an exothermic chemical rxn proceed in the opposite direction, it becomes an endothermic rxn that absorbs energy. Similarly if an endothermic rxn proceeds in the opposite directions it becomes an exothermic rxn that release energy

Investigative Lab : 

Investigative Lab “Exothermic or Endothermic” TE/PE pp92-93 Question: Material: Procedure: What do you think?:

Sections 3.4Life and Industry depends on chemical reactions : 

Sections 3.4Life and Industry depends on chemical reactions Living things require chemical reactions; Chemical reactions are used in technology Industry uses chemical reactions to make useful products

Section 3.4 Objective : 

Section 3.4 Objective The Student will: Define Key vocabulary; Identify the relationship between the reactions of respirations and the reactions of photosynthesis Recognize how chemistry has been used to develop new technology Infer through an experiment how catalysts affect a chemical reaction

Warm-Up : 

Warm-Up Transparency 21 overhead Match the definition to the correct term

Vocabulary : 

Vocabulary none

Investigate Lab : 

Investigate Lab “sugar combustion ” Question: How are catalysts important in the combustion of sugar Material: Candle * matches * tongs * 2 sugar cubes * ashes Procedure: Using the tongs hold a sugar cube in a candle flame for 30 seconds observe what happens Rub ashes on the second sugar cube Using the tongs, hold the second sugar cube in the candle flame for 30 seconds. Observe what happens What do you think?: What happened to the first sugar cube? What may have caused any differences that you observed? Challenge: How might the ashes used in this experiment have a similar fxn to enzymes in your cells? explain

Overview : 

Overview Respiration, photosynthesis will be covered at a later date You are to work in groups and provide a presentation on one of the following Chemical rxn used in technology Chemical rxn used in useful products