Chemical Reactions: ATI Exam
2AgNo3+Cu-Cu(NO3)2+Ag Now that the nitrate is balanced in the equation but there are two times as many silver atoms amoung the reactants compared with the products we can resolce that by adding
2 as a coefficient to the silver metal on the roduct side of the equation. 2AgNo3+ Cu- Cu(NO3)2 +2Ag now our equation is balanced.
Acids are substances that have a pH less than
7.
Bases have a pH greater than
7.
The general formula for a double replacement reaction is:
A+B-+C+-____A+D-+C+B- you can see that cations A+ and C+ switch places ( double replacement), forming two new ionic compounds for example, if we stick with AgNO3 but this time react it with KCl we get: AgNO3+KCl___AgCl+KNO3
The general equation for a single replacement reaction is:
AB(aq) + C- A+CB(aq) This says that the coumpound AB, which is dissolved in water (aq or aqueous) and the element C react to form a new compound Cb dissolved in water and the pure element A.
Combustion is a type of redox reaction in qhich 02 and a little bit of heat or energy convert a substance to
CO2 and H20 generating a lot of heat, for example, the combustion reaction for burning gasoline in an automobile is: 2C8H18+2502---16C02+18H20+ heat/energy.
The pH scale is a measure of the
H+ concentration (written as [H+]) in an aqueous solution, specifically, pH= -log [H+]. The pH scale runs from 0 to 14, it is a logarithmic scale, meaning that every integer increase, say from 1 to 2 or 9 to 10, is a tenfold increase in [H+].
Oxidation-reduction reactions are an important and familiar class of chemical reactions, often abbreviated as redox reactions, these are the basis of rust formation, combustion, and energy formation in our cell, a rebox reaction involves
a transfer of electrons between two chemical species, one of the species gains electrons from the other substance that give upelectrons, we have seen an example of this in an earlier section, when we discussed single displacement reactions, lets look again at the reaction 2AgNO3+Cu---Cu(NO3)2+2Ag
Enzymes are complex organic molecules that function as catalysts, molecules that increase the rate of a chemical reaction by lowering the activation energy , without themselves being permanently chemically altered in the process, enzymes are
absolutely essential for life, because without them, many of the reactions in our bodies either would never happen or would take far too long to support life.
The general equation for an acid-base reaction is:
acid+base--salt + water which we can also write as: HA+BOH---AB+H20..
If we read the equation in words, it says to mix two atoms of silver nitrate with one atom of copper metal, (wait a few hours)
and one atom of copper nitrate and two atoms of silver metal are formed.
Chemical reactions happen between atoms, molecules, or compounds. a molecule is any arrangement of two or more
atoms bonded together, water, H20, is a molecule; so are carbon dioxide (C02) ethanol (CH3CH2OH) , H2, and O2. these are all molecules,
2AgNO+Cu--Cu(NO3)2+2Ag when AgNO3 is dissolved in H20, the Ag+ cations and the NO3- anions are in a sea of polar H20 molecules, some of the Ag+ cation are
attracted to the partially negative 0 in H20 and some of the NO3- anions are attracted to the partially postie H's some of the Ag+ and NO3- ions continue to interact; but in solution, it is a constantly moving dance of ions and water moleules..
Electrogativity is the tendency of an atom ( or small group of atoms) to attract elctrons, An ionic bond forms between an atom with lw electronegativity (which readily gives up an electron). The result is the formation of two ions held together by an ionic bond, for example,
combining lithium (an alkai metal) and fluorine (a halogen) rapidly produces lithium fluoride. LiF is stable because the cation Li+ and the anion F- each have a full outer valence shell of electrons. Other ionic compounds include familiar salts, like NaCl (sodium chloride) , KCl (potassium chloride) and NaHCO3 (sodium bicarbonate).
Reactions are affected by the
concntrations of reactants and products, the temperature, pressure, and pH of the reaction conditions, and whether a catalyst is present.
Molecules in solution or gaseous form are in
constant motion, chemical reactions occur when individual molecules get close enough to each other for their valence shell electrons to interact or to be drawn toward the nucleus of the nearby atom. as temperature increase, molecules move faster, so they are more likelt to "bump into each other" thus, in general, raising temperature increases the formation of products. If temperature rises, then the rate of an endothermic reaction (where heat is a reactant) will increase. when the reaction is exothermic (where heat is a product), the reaction will slow down or the reverse reaction will prevail.
The creation of an aqueous solution of silver nitrate makes it much easier for the ions floating around in solution to interact with elemental copper, Copper donates
electrons to the Ag+ anions which converts Ag+ to the neutral silver atom. because copper has lost electrons, it becomes a cation, Cu2+ (note that copper readily loses two electrons giving one to each of two Ag+ cations) the elemental silver begins to precipitate out of the soution, and Cu2+ begins to interact with N03- FORMING A NEW SOUTION, BLUE COPPER NITRATE SOLUTION.
Atoms are the fundamental units of the
elements, atoms combine to fotrm stable molecules, and molecules react with one another to form new molecules.
Neural atoms contains an
erqual number of protons and electrons. Such an atom is neutral because the postive charges of the protons are balanced by the negative charges of the electrons.
Our bodies also carry out combustion reactions, these occur in our cells and are used to
generate chemical energy (mostly as ATP) that can drive cellular work, the fuel we burn is glucose and related sugar compounds, but instead of creating masive amounts of heat all at once and losing most of the energy as heat, our cells carry out the oxidation-reduction reaction as a series of smaller reactions that gradually release the chemical energy held in the bonds of glucose, the combustion of glucose is: C6H1206+602---A06C02+6H20+ heat/energy.
Chemical reactions do not all happen at the same rate, some reactions are explosive, and some happen so slowly they are measured in
hours, days or even years, for example, drop potassium metal (K) into water to enjoy a massive explosion. rust formation is a very slow chemical reaction: 4Fe+302--Fe203 but importantly, for any given reaction there are several conditions that affect the rate of the chemical reaction.
Chemical reactions are occurring constantly literally everywhere,
inside human body cells, in the air, water and soil.
What does it mean to have a partial charge?
let's look at a water moecule, on the left is a model of H20, showing that the hydrogens are covalently bonded at an angle to the central oxygen, on the right is H20 shown as a stick figure with symbols above each atom indicating a partial charge.
A solution that is at pH 7 is a
neutral solution.
AgNO3+Cu- Cu(NO3)2 +AG we begin by writing the reactions and products in the reactin, there is one silver atom on both sides of the equation so that is okay, this is also
one copper atom on both sides of the equation, so that is balanced as well, but there is one nitrate molecule on the reactant side of the equation but two nitrate moleules on the product side. (the reason is that copper binds two molecules of nitrate to form copper nitrate, while silver nitrate is formed form equal amounts of silver and nitrate.) we can't assume that nitrate just appeared. it had to come from the siliver nitrate solution, so the amount of nitrate on both sides has to be made equal. we can do that by starting with twice as mcuh AgNo3.
We divide acids into strong acids and weak acids, the stronger the acid, the lower the
pH, similary, there are strong and weak bases, the stronger the base, the higher the pH.
The substances on the right side of the equation are the
products , the things that are formed.
All chemical reactions involve breaking and forming of bonds to create new substances, but there are many different ways that chemical reactions occur depending upon the
reactants themselves, the concentrations (amount) of the reactants, conditions such as temperature, pressure , and PH and whether a catalyst is present.
The substances on the left side of a chemical equation are the
reasctants the things that you start with.
An arrow separated reactants and products note that the equation above is balanced menaing that there is the
same nuber of each type of atom on both sides of the equation, lets look at this more closely, beause understanding how to balance chemical equations is very important.
An exaple of a chemical reaction is the precipitaion of silver and formation of copper m=nitrate soluion by combining
silver nitrate and copper, we depict this reaction by writing a chemical equation, 2AgNO3+Cu-Cu(NO3)2+ you can preform this reaction quite easily, AgNO3 is an inexpensive compound that dissolves in water, if you drop a copper rod into the silver nitrate solution and set it aside for a few hours, crystals of pure silver form on the surface of the copper rod, the solution meanwhile turns blue becuase it changes from silver nitrate to copper nitrate, these roducts appear because the bonds holding Ag to NO 3 are breoken while bonds between Cu and NO3 are being formed.
Ionic salts dissove readily in water, which causes the ions to dissociate from one another, the result is a
solution of anions and cations that can undergo a number of chemical reactions. one class of these is the double replacement reaction.
A chemical reaction is a process that exchanges one bonding arrangement among atoms for a different bonding arrangement, for this to happen
some bonds between atoms have to be broken and new bonds have to form.
The reaction in the previous example 2AgNo3+Cu-Cu(NO3)2 +2Ag is a single replacement reaction, in a manner of speacking the silver and copper have
swiched places, the silver in the silver nitrate makes way for the copper which bonds with the nitrate to form copper nitrate, so copper has replaced silver in the compound, which is the essence of a single replacement reaction: one element is subsituted for another element in a compound.
A base is a compound that has the
tendency to accept a proton, an acid-base reaction is a type of double displacement reaction in which a proton (H+) and hydroxide ion (0H-) combine to form H20 for example: H2S04+2KOH--- A0K2S04+2H20.
An acid is a coumpound that has a
tendency to transfer a proton to another molecule.
Now let's examine this reaction more closely AgNO3 is available as a solid ionic salt, it is an ionic compound that dissolves readily in water, dissolution means
that the ions that make up the solid compound are pulled apart and coate with water molecules, we need to digress for a moment.
Increasing the concentration of reactants increases the probability that reactants will come in contact with each other, therefore increasing the liklihood of breaking or creating a bond, if product concentration is increased,
the reaction will slow down, on the other hand if products are withdrawn from the reaction as they form, then the rate of product formation increases, for gaseous molecules, increasing the pressure drives molecules closer together, so by the same reasoning used with temperature, an increase in pressure will increase the number of interactions between reactant molecules and thus increase the rate of the reaction.
Sythesis and decompostion reactions are fundamental to biochemistry, organisms ( like humans) consume food for two purposes,
they use it as an energy source and as building blocks to make complex organic molecules, for example, humans consume proteins in our diet, Enzymes in our digetive system decompose (or break down) the proteins into various amino acids and other nitrogenous compounds, which are absorbed into our blood and carried to cells throughout the body, inside our cells , these building blocks interact with different enzymes to synthesize the complete set of twenty amino acids, these amino acids are used to build proteins inside our cells.
Why would charged anions and cations be coated or surrounded by water, H20?
this is beacuse water, which is made of two hydrogen atoms covalently bonded to an oxygen atom, contains a partial charge.
One type of bond is the ionic bound, which results when
two atoms have a large electronegative difference between them, such as between metals and nonmetals.
Water forms because oxygen is a highly electronegative element that needs tow electrons to complete its valence shell of electrons, each hydrogen atom readily shares its lone electron and oxygen gets the
two electrons it craves, but even though water is a covalent neutral (uncharged) molecule, the electronegative oxygen hogs the shared electrons, most of the time, the electrons are closer to the oxygen nucleus than they are to the hydrogen nuclei, this is symbolized as &- (delta minus) above the oxygen atom. The &+ (delta plus) means that the hydrogen atoms are partiallt cationic; they have a partial postive charge thus we say, that water is a covalent polar molecule,
A compound is any molecule that contains
two or more elements, so H20, C02 an C6H1206 ( glucose) are all compounds, but H2 and O2 ( molecular hydrogen and molecular oxygen) are not.
Synthesis and decomposition reactions are essentially opposing reactions, in a synthesis reaction
twodifferent substances combine to form a more complex product, in a decompostion reaction, that complex product is broken down into its constituent parts, for example, lets make and destroy water, Sythesis of water: 2H2+O2-----2H20 Decompostition of water: 2H20-----2H2+02
The number of electrons in a redox reation doesn't change. what changes is
where the electrons are located, so every, oxidation in a reaction is simultaneously accompanied by a reduction, when Ag+ becomes reduced, Cu is oxidized..
