Presentation on theme: "Chemical Reactions Alter Arrangements of Atoms"— Presentation transcript:
1Chemical Reactions Alter Arrangements of Atoms Section 7-1
2Atoms interact in chemical reactions. How does a chemical reaction produce a new substance?By changing the way the atoms are arranged. Bonds between atoms are broken and new bonds form. This happens when particles collide.
3Physical ChangesA physical change is a change in the state (phase) of a substance.What are the three states of matter?Solid, Liquid, and Gas
4What happens when a substance undergoes a physical change? Its physical form changes but the substance itself remains unchanged.
5What is electrolysis?The process by which water breaks down into hydrogen and oxygen molecules.How can you tell that splitting water to form hydrogen and oxygen is a chemical change? How does this change occur?New substances form with new and different properties. Bonds break and new bonds form.
6Chemical Vs. PhysicalHow is a chemical change different from a physical change?During a chemical change the original substances turn into different substances. In a physical change, the original substances still keep their original properties.
7Reactants and Products Reactant – the substances present at the beginning of a chemical reaction.Product – the substances formed by the chemical reaction.
8Reactants and Products What must happen for a reactant to be changed into a product?The bonds in the reactants must be broken and new bonds must form in the products.
9Evidence of a Chemical Reaction Color ChangeFormation of a precipitateFormation of a gasTemperature change –gives off heat or light
10Evidence of a Chemical Reaction How can temperature change in a chemical reaction be observed without using a thermometer?Seeing a flame or feeling warmth (production of heat or light).
113 Types of Chemical Reactions: Synthesis Reaction – a new compound is formed by the combination of simpler reactantsDecomposition Reaction – a reactant breaks down into simpler productsCombustion Reaction – one reactant is always oxygen, the other often contains carbon or hydrogen.
123 Types of Chemical Reactions: Synthesis Reaction means “making a substance from simpler substances.”Decomposition Reaction means “separation into parts.”Combustion Reaction is the process of burning with oxygen.
133 Types of Chemical Reactions: How are synthesis reactions different from decomposition reactions?Synthesis reactions make more complex products from simpler reactants.Decomposition reactions break down complex reactants into simpler products.
14Synthesis ReactionTwo or more simple substances combine to form a new, more complex substance.A B C2 reactants product
16Decomposition Reaction A complex substance breaks down into two or more simpler substances.C A B1 reactant 2 products
17Decomposition Reaction Example C12H22O11 11 H2O +12CSugar heat Water CarbonH2CO3 H2O + CO2Carbonic Acid
18The rates of chemical reactions can vary. The three physical factors that affect the rate of a chemical reaction are concentration, surface area, and temperature.The chemical factor that affects reaction rate is called a catalyst
19ConcentrationConcentration measures the number of particles present in a certain volume.
20Surface AreaWhy does a reaction proceed faster when the reactants have a greater surface area?More particles are available to collide and react when the surface area is greater.
21TemperatureThe rate of a reaction can be increased by making the particles move faster.Why are collisions between particles important in chemical reactions?Particles of reactants must collide to react.
22CatalystsDefinition – a substance that increases the rate of a chemical reaction but is not itself consumed by the reactionCharacteristics – remains unchangedExample – EnzymesNon-Example – something that slows the reaction or is changed/consumed by the reaction.
23ReviewHow might the chewing of food be related to the rate of a chemical reaction, digestion, that occurs in your body? Explain your answer.
24ReviewHow might the chewing of food be related to the rate of a chemical reaction, digestion, that occurs in your body? Explain your answer.Chewing increases the surface area of food which speeds up chemical reactions involved in digestion.
25The mass of reactants and products are equal. Ch. 7.2 NotesThe mass of reactants and products are equal.
26The mass of reactants and products are equal. Careful observations led to the discovery of the law of conservation of mass.
27Describe the Law of Conservation of Mass Lavoisier found that atoms can never be created or destroyed in a chemical reaction.Most reactions that seem to gain or lose mass actually involve reactions with gases.The mass of the reactants is always equal to the mass of the products.
28Why is mass conserved in a chemical reaction? Atoms are not created or destroyed in a chemical reaction.
29200g of reactant A and 100g of reactant b are combined to form a new substance- Product C. What is the mass of product C?350 g
30How did Lavoisier investigate the conservation of mass How did Lavoisier investigate the conservation of mass? Why did he use sealed containers in his experiments?By carefully observing and measuring all of the reactants and products in chemical reactions, he found that the total masses were always equalHe could measure the total mass of the air and the mercury instead of just the mass of the mercury.
31Chemical reactions can be described by ____________ __________________.
32How does a chemical equation show the conservation of mass? By showing on each side of the equation the same number of atoms of each element involved in the reaction.
33In order to write a chemical equation, what information do you need to know? The reactants and products in the reactionThe atomic symbols and chemical formulas of the reactants and products in the reactionThe direction of the reaction
34C + O2 CO2 Reactants Product Write the chemical equation represented by the following sentence. Carbon (C) reacts with oxygen (O2) to yield carbon dioxide (CO2). Label the reactants and products.C + O2 CO2Reactants Product
36Is the equation below balanced? Why or Why not? H2 + O2 H2ONo, the equation has only one oxygen atom on the right side and two oxygen atoms on the left side.
374 steps to balancing equations: Write chem. Equation with correct symbols & formulasWrite the number of atoms of each element on each side of the equation. (Write the # very small under the symbol)Balance atoms by using coefficients(large # in front of symbol or formula, then change # under symbol)Check by counting the numbers of atoms of each element.
384 steps to balancing equations: Cont.*DO NOT CHANGE SUBSCRIPTS!!!!**Oxidation numbers in a compound must add up to equal zero.*When adding a subscript to a polyatomic ion, you must put the polyatomic ion in parenthesis first.*The total number of atoms on both sides of the equation must be the same [(Law of conservation of mass: mass remains constant in a chemical reaction) (mass is neither created nor destroyed; it only changes form.]
39Using Coefficients to Balance Equations Why can you change coefficients to balance an equation but not subscripts?Subscripts are part of a chemical formula, while coefficients just show the number of molecules involved.
40Chemical reactions involve energy changes. Ch. 7.3 NotesChemical reactions involve energy changes.
42The amount of energy in a chemical bond between atoms Bond energyThe amount of energy in a chemical bond between atoms
43For each reaction, write absorbed or released. a. Breaking bonds: energy is absorbedb. Forming bonds; energy is releasedc. Endothermic: energy is absorbedd. Exothermic: energy is released
44Exothermic ReactionsDefinition: a chemical reaction that releases energyCharacteristics: often causes an increase in temperature; energy is released as heatExample: rocket blasting offNonexample: photosynthesis
45Endothermic ReactionDefinition: a reaction in which energy is absorbedCharacteristics: energy must be added to the reaction, often causes a drop in temperatureExample: photosynthesisNonexample: rocket blasting off
47Describe exothermic reactions Exothermic reactions release energyBond energies of the reactants are less than the bond energies of the productsSome reactions produce a lot of heatAll common combustion reactions are exothermicExothermic chemical reactions also occur in living things.
48The picture below shows a common chemical reaction. Is the reaction exothermic or endothermic? How do you know?
49The picture below shows a common chemical reaction. Exothermic; It is releasing energy (heat)
50Describe the bond energies in an exothermic reaction. The bond energies of the reactants are less than the bond energies of the products.
52Describe Endothermic reactions Endothermic reactions absorb energy.The energy difference is usually absorbed as heat;Photosynthesis is probably the most important series of endothermic reactions
53IV. Exothermic and endothermic reactions work together to supply energy.
54How does the combination of endothermic and exothermic reactions help us use energy from the sun? Energy from the Sun is stored by endothermic reactions (photosynthesis) and released by exothermic reactions (combustion)
56Answers to review questions: Exothermic reactions; products have higher bond energy than reactants and energy is released; endothermic reactions: reactants have higher bond energy than products and energy is absorbed.Exothermic; energy is released as heat and light
57Answers to review questions: Endothermic: energy from light is absorbed in order for the reaction to occur.They are approximately opposite reactions in terms of energy as well as reactants and products
58Answers to review questions: Fossil fuels contain the carbon stored in plants by photosynthesis hundreds of millions of years ago. So, energy in fossil fuels started as energy from the Sun.Bond energy is greater in the reactants; when the reaction is reversed, the bond energy is greater in the products and energy is released.