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Chapter 2 Chemical Reactions
Chemistry – Chemical Reactions
When bonds between atoms are broken or formed it is said that a chemical reaction has
occurred.
- chemical reactions take place at electron bonds or within electron shells.
- reaction is divided into two parts: reactants and products
reactants are the starting molecules or atoms of a reaction
products are the end results of the reaction.
- in between both reactant and product is the directional arrow.
- gives direction of reaction
- can be one way: → or ←
- can be two way (bidirectional): ↔
e.g. 2H2 + O2 → 2H2O
reactants
product
- the same amount of atoms that go into the equation will appear in the product.
Forms of Energy and Chemical Reactions
Energy – the ability to do work. There are 2 types:
potential energy – stored energy
kinetic energy – energy of movement
Chemical energy is (a type of potential energy) – stored energy found in bonding
between atoms in molecules and compounds.
-energy is transformed from one form to another.
Law of Conservation of Energy
-energy may be converted from one form to another, but the total quantity
of energy remains constant.
e.g. foods that we eat are stored energy that are broken down and
and their chemical components are used in body functions
such as walking, talking, breathing, and body temperature
regulation. etc.
Energy Transfer in Chemical Reactions
Energy – the ability to do work
2 Types: Potential Energy – stored energy
Kinetic Energy – energy of movement
Chemical Energy – a type of potential energy found in bonding between
atoms in molecules and compounds.
Note: energy is transformed from one form to another. This is called >>>>
Law of Conservation of Energy – energy may be converted from one form to another, but
the total quantity of energy remains constant.
e.g. foods that we eat are stored energy that are broken down and their
chemical components are used in body functions.
Energy Transfer in Chemical Reactions
Chemical Reactions can lead to 2 types of reactions:
Exergonic Reactions – occur when a chemical reaction releases energy.
Endergonic Reactions – occur when a chemical reaction absorbs energy.
-they often work together within the body to create either body structures
or body motion.
In order to break bonds and or create new bonds – Activation Energy is needed.
Activation Energy is the energy required to break bonds in a reactant molecule.
- this causes a reaction..
2 requirements: Concentration of Matter – more matter, more collisions
Temperature – higher temperature, faster collisions
Catalysts are also needed to save or reduce the amount of energy needed.
-catalyst in the human system is called enzymes.
-enzymes are proteins that:
-speed up reactions
-are reusable
-very efficient
Types of Chemical Reactions
1. Synthesis Reaction – Anabolism (Endergonic)
A + B → AB
2. Decomposition Reaction – Catabolism (Exergonic)
AB → A + B
3. Exchange Reaction
AB + CD ↔ AD + BC
4. Reversible Reaction
AB ↔ A + B
Inorganic Compounds and Solutions
-relatively small, simple substances that usually do not contain carbon.
e.g. NaCl, KI
-a few inorganic compounds do contain carbons.
e.g. CO2, CO, HCO3Water –important substance for all living organisms.
-70% of human body weight
-85% of brain
-important in many chemical reactions in living systems.
-has unique properties that also affect the environment.
Properties of Water
1. Excellent Solvent – polarity makes water capable of dissolving many
different kinds of substances especially polar
compounds. e.g. H2O + NaCl
-because of partial charge of water, it pulls ions of
ionic compounds apart so that they dissociate.
Note: Solutions are substances that are composed of: solvent ( H2O) and solute (solid).
Solvent dissolves solute.
-a solution usually contains more solvent than solute (dilute)
-when more solute than solvent, it is saturated.
-solutes that have polarity are hydrophilic (dissolve)
e.g. salt, sugar
-solutes that are non polar are hydrophobic (do not dissolve)
e.g. fats, oils
2. Water in Chemical Reactions –important for breaking down or building
up molecules.
- 2 Types: a) Hydrolysis –water is used to split larger molecule.
b) Dehydration –water is removed to form larger molecule.
3. Thermal Properties :
a) has high specific heat (heat capacity), a result of H bonding.
-helps maintain stable temperature because it can hold heat.
b) high heat of vaporization – to change 1 gram of water into 1
gram of vapor (steam), 540 calories of heat are required.
(calories are units of heat energy) – in other words, it takes
a lot of energy to convert a small amount of a substances
such as water.
4. Water as a Lubricant –important for ease of movement.
e.g. synovial fluid, saliva, and serous fluid
Acids, Bases, Salts
-in solution, acids, bases, and salts dissociate into ions.
a) Acids – a substance that dissociates in solution to yield H+ ion
and an anion when dissolved in water.
-proton donor
-produces a sour taste
e.g. hydrochloric acid, sulfuric acid, lactic acid, acetic acid
b) Bases –a substance that dissociates to yield an OH- ion and a cation
when dissolved in water.
-proton acceptor
-is slippery to touch
e.g. sodium hydroxide, ammonium
hydroxide,purines and pyrimidines (found in
DNA)
Note: pH –a scale that indicates a solution’s acidity or basicity.
_______________________________________________________
0
7
14
acidic
neutral
basic
-it ranges from 0 to 14, with 7 indicating neutrality.
-as pH decreases below 7, a solution is more acidic.
-as pH increases above 7, a solution is more basic.
e.g. gastric juices – pH 2
pure water – pH 7
household ammonia – pH 11
c) Salt –a compound in which H atoms of an acid and OH of a base are
replaced to form a new compound.
-can occur with just acid or base or combination of both.
e.g. NaOH + HCl → NaCl + H2O
-when salt, acid, and base are dissolved in water, they dissociate
into charged particles.
-these particles can conduct an electrical current – electrolytes.
-salts provide the many mineral ions essential for fluid balance,
nerve and muscle functions etc.