Chemical Reactions – Part II Five Types of Chemical Reactions
Chemical Reactions
description
Transcript of Chemical Reactions
![Page 1: Chemical Reactions](https://reader036.fdocuments.in/reader036/viewer/2022062520/568163a2550346895dd4a1c9/html5/thumbnails/1.jpg)
CHEMICAL REACTIONSChapter 21
![Page 2: Chemical Reactions](https://reader036.fdocuments.in/reader036/viewer/2022062520/568163a2550346895dd4a1c9/html5/thumbnails/2.jpg)
• Chemical reactions are taking place all around you and even within you.
• A chemical reaction is a change in which one or more substances are converted into new substances.
Describing Chemical Reactions
A chemical reaction occurs when you bake a cake.
![Page 3: Chemical Reactions](https://reader036.fdocuments.in/reader036/viewer/2022062520/568163a2550346895dd4a1c9/html5/thumbnails/3.jpg)
Physical Change Change that alters the form of a
substance but not the composition Tearing of paper Chopping wood Melting ice Change of state Dissolving
![Page 4: Chemical Reactions](https://reader036.fdocuments.in/reader036/viewer/2022062520/568163a2550346895dd4a1c9/html5/thumbnails/4.jpg)
Chemical Changes Result of a chemical reaction Breaking of bonds and formation of new
bonds Atoms are rearranged Energy is released or absorbed
![Page 5: Chemical Reactions](https://reader036.fdocuments.in/reader036/viewer/2022062520/568163a2550346895dd4a1c9/html5/thumbnails/5.jpg)
Examples of Chemical Reactions
Combustion – substance and oxygen are combined and release heat or light
Metabolism – chemical change that releases energy through digestion
Fermentation – break down of carbohydrates by living things in the absence of oxygen
Corrosion- Rusting Electrolysis
![Page 6: Chemical Reactions](https://reader036.fdocuments.in/reader036/viewer/2022062520/568163a2550346895dd4a1c9/html5/thumbnails/6.jpg)
Signs of a Chemical Reaction
Rapid release of energy– heat, light, sound
Production of a gas– bubbles Forming a precipitate– a solid that
doesn’t dissolve in liquid Substance getting colder Examples: Fire, antacid tablet in water,
rusting, silver tarnish
![Page 7: Chemical Reactions](https://reader036.fdocuments.in/reader036/viewer/2022062520/568163a2550346895dd4a1c9/html5/thumbnails/7.jpg)
Exothermic/Endothermic More energy is
produced than it takes to break the bonds of the reactants
Energy is released from the reaction
Gives off heat and/or light
Fire MRE’s – wrapped in
special sleeve with Mg – addition of water starts reaction that heats food
Takes more energy to break bonds in the reactants than is released by forming products
Energy has to be put in for the reaction to occur
Gets colder Instant ice pack – water
and ammonium nitrate Rusting iron
![Page 8: Chemical Reactions](https://reader036.fdocuments.in/reader036/viewer/2022062520/568163a2550346895dd4a1c9/html5/thumbnails/8.jpg)
Conservation of Mass
• For example, the mass of the candles and oxygen before burning is exactly equal to the mass of the remaining candle and gaseous products.
• The French chemist Antoine Lavoisier established that the total mass of the products always equals the total mass of the reactants.
![Page 9: Chemical Reactions](https://reader036.fdocuments.in/reader036/viewer/2022062520/568163a2550346895dd4a1c9/html5/thumbnails/9.jpg)
• One of the questions that motivated Lavoisier was the mystery of exactly what happened when substances changed form.
Lavoisier's Contribution
• He began to answer this question by experimenting with mercury.
![Page 10: Chemical Reactions](https://reader036.fdocuments.in/reader036/viewer/2022062520/568163a2550346895dd4a1c9/html5/thumbnails/10.jpg)
• Lavoisier placed a carefully measured mass of solid mercury (II) oxide, which he knew as mercury calx, into a sealed container.
Lavoisier's Contribution
• When he heated this container, he noted a dramatic change.
• The red powder had been transformed into a silvery liquid that he recognized as mercury metal, and a gas was produced.
![Page 11: Chemical Reactions](https://reader036.fdocuments.in/reader036/viewer/2022062520/568163a2550346895dd4a1c9/html5/thumbnails/11.jpg)
• When he determined the mass of the liquid mercury and gas, their combined masses were exactly the same as the mass of the red powder he had started with.
Lavoisier's Contribution
• Lavoisier also established that the gas produced by heating mercury(II) oxide, which we call oxygen, was a component of air.
![Page 12: Chemical Reactions](https://reader036.fdocuments.in/reader036/viewer/2022062520/568163a2550346895dd4a1c9/html5/thumbnails/12.jpg)
Conservation of mass the mass of the reactants will always
equal the mass of the products in a closed system(you have to “catch all of the products”
2H2 + O2 = 2H2O H – 1.01 amu O – 16 amu Reactants Products 4H – 4.04 2H2O – 36.04 2O – 32 amu Total – 36.04 amu
![Page 13: Chemical Reactions](https://reader036.fdocuments.in/reader036/viewer/2022062520/568163a2550346895dd4a1c9/html5/thumbnails/13.jpg)
Conservation of atoms the number of atoms in the reactants will
always equal the number of atoms in products in a closed system
2H2 + O2 = 2H2O Reactants Products 4H 4H 2O 2O
![Page 14: Chemical Reactions](https://reader036.fdocuments.in/reader036/viewer/2022062520/568163a2550346895dd4a1c9/html5/thumbnails/14.jpg)
• Scientists have developed a shorthand method to describe chemical reactions.
Writing Equations
• A chemical equation is a way to describe a chemical reaction using chemical formulas and other symbols.
• “Recipe” for chemical reactions • Bonds are breaking and reforming• CH4 + O2 → CO2 + H2O + heat + light
• Methane and oxygen yield carbon dioxide and water
• One or more substance (reactants) change into one or more new substances (products)
![Page 15: Chemical Reactions](https://reader036.fdocuments.in/reader036/viewer/2022062520/568163a2550346895dd4a1c9/html5/thumbnails/15.jpg)
• Reactants to the left of the arrow
• Products to the right of the arrow
• Arrow is yields• Reactants yield the
products• Some of the symbols used
in chemical equations are listed in the table.
• Example: (aq) stands for aqueous, which means dissolved in water
Writing Equations
![Page 16: Chemical Reactions](https://reader036.fdocuments.in/reader036/viewer/2022062520/568163a2550346895dd4a1c9/html5/thumbnails/16.jpg)
Balanced Equations
• Lavoisier's mercury(II) oxide reaction can be written as:
• Notice that the number of mercury atoms is the same on both sides of the equation but that the number of oxygen atoms is not the same.
![Page 17: Chemical Reactions](https://reader036.fdocuments.in/reader036/viewer/2022062520/568163a2550346895dd4a1c9/html5/thumbnails/17.jpg)
Balanced Equations Start with a skeleton equation like Lavoisier’s
Each side of the equation must have the same number of atoms of each element
We use coefficients to balance equations – (whole number in front of the chemical formula)
H2 + O2 → H2O 2H2 + O2 → 2H2O
![Page 18: Chemical Reactions](https://reader036.fdocuments.in/reader036/viewer/2022062520/568163a2550346895dd4a1c9/html5/thumbnails/18.jpg)
Balancing Two things you CANNOT do when
balancing an equation
You cannot change a subscript
You can only write the coefficient in front of a chemical formula
![Page 19: Chemical Reactions](https://reader036.fdocuments.in/reader036/viewer/2022062520/568163a2550346895dd4a1c9/html5/thumbnails/19.jpg)
Limiting and Excess Reactants Limiting Reactant – the reactant that is
used up first limits the amount of product
Excess Reactant – the reactant that is not completely used up because there is extra
If I have 1 cup flour and 2 eggs but only need 1 egg for my recipe – the flour is the limiting reactant and the egg is the excess reactant
![Page 20: Chemical Reactions](https://reader036.fdocuments.in/reader036/viewer/2022062520/568163a2550346895dd4a1c9/html5/thumbnails/20.jpg)
Inhibitors and Catalysts Catalysts speed up reactions. They do
not change what goes in or comes out, but they make the reactions happen faster- example- enzymes
Catalysts are often affected by other factors such as pH and temperature
Inhibitors slow down reactions– such as food preservatives that help keep food from spoiling too quickly
![Page 21: Chemical Reactions](https://reader036.fdocuments.in/reader036/viewer/2022062520/568163a2550346895dd4a1c9/html5/thumbnails/21.jpg)
Types of reactions Combustion Synthesis (Addition) Decomposition Single Displacement (Single
Replacement) Double Displacement (Double
Replacement)
![Page 22: Chemical Reactions](https://reader036.fdocuments.in/reader036/viewer/2022062520/568163a2550346895dd4a1c9/html5/thumbnails/22.jpg)
Combustion A chemical reaction in which something is
burned Lavoisier was one of the first to observe
this type of reactions A combustion reaction occurs when a
substance reacts with oxygen to produce heat and/or light
C6H12O6 + 6O2 6CO2 + 6H20 Products are always the same
![Page 23: Chemical Reactions](https://reader036.fdocuments.in/reader036/viewer/2022062520/568163a2550346895dd4a1c9/html5/thumbnails/23.jpg)
Synthesis Reactions Also called addition Two or more substances combine to form
another substance General Formula: A + B AB Example: 2H2 + O2 2H20
![Page 24: Chemical Reactions](https://reader036.fdocuments.in/reader036/viewer/2022062520/568163a2550346895dd4a1c9/html5/thumbnails/24.jpg)
Decomposition A substance breaks down, or decomposes
into its components General Formula: AB A + B Example: 2H20 + 2H2 + O2
![Page 25: Chemical Reactions](https://reader036.fdocuments.in/reader036/viewer/2022062520/568163a2550346895dd4a1c9/html5/thumbnails/25.jpg)
Single Displacement Also called single replacement One atom displaces, or replaces another
to form a new substance General Formula: A + BC AC + B Example:
Cu (s) + 2AgNO3 (aq) Cu (NO3)2 + 2Ag (s)
![Page 26: Chemical Reactions](https://reader036.fdocuments.in/reader036/viewer/2022062520/568163a2550346895dd4a1c9/html5/thumbnails/26.jpg)
Double Displacement Also called double replacement The positive ion of two compounds switch
with each other, making two entirely new compounds
General Formula: AB + CD AD + CB Example:
Ba (NO3)2 (aq) + K2SO4 (aq) BaSO4 (s) + 2KNO3 (aq)