Section 1
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What does the differential rate law first order graph look like?
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Section 1
(50 cards)
What does the differential rate law first order graph look like?
Length of half life is constant. *For first order reactions, the half life is independent of the initial concentration of reactant.
What and where is the activated complex?
Activated Complex = Transition state. At the transition state, the particles can either fall to reactants or fall back to the products.
What are the factors that affect rxn rates?
1. Nature of Reactants: solids will react much more slowly than liquids or aqueous solutions // ions of opposite charge react very rapidly // the MORE BONDS between reacting atoms = SLOWER rxn rate because more energy is required to separate. 2. Concentration: more molecules present = more COLLISIONS = faster rxn = greater rate. 3. Temperature: faster the molecules move = more likely to collide = greater rxn rate. // Increasing temperature increases the number of particles that have enough energy to have a successful COLLISION (i.e. more energy than Ea) // 10ºC increase will DOUBLE RXN RATE. 4. Surface area of reactants: the greater the surface area exposed, the greater chance of collisions between particles. 5. Adding an inert gas (NOBLE GASES) have NO effect on the RATE or EQUILIBRIUM of rxn. It's not in the rxn mechanism. 6. Catalyst: A catalyst is NEVER CONSUMED and can be used OVER AND OVER AGAIN. It could become less effective by altering pH or temperature.
What is the rate constant k?
K is temperature dependent and must be evaluated by experiment.
Elements with high ionization energies have high electron affinities.
Giving an element with a high IE an e- will make it super stable and release energy.
What does the differential rate law second order graph look like?
Length of half life increases with decreasing concentration.
Explain: the normal boiling point of CCl4 is 77ºC, whereas that of CBr4 is 190ºC.
CCl4 and CBr4 are both covalent compounds that have London Dispersion Forces. CBr4 is a bigger molecule, therefore it has more electrons, and is more polarizable. Since CBr4 is more polarizable, it has greater LDFs, which lead to a higher boiling point.
Explain why solid K conducts an electric current, whereas KNO3 does not?
Solid K conducts electricity because of its metallic bonding. Metals can conduct e- as solids. KNO3 cannot conduct electricity because ions are not mobile, so they cannot carry charge. *Ionic compounds can only conduct e- when molten or dissolved in water.
Explain: NH3 is very soluble in water whereas PH3 is only moderately soluble in water.
Ammonia has hydrogen-bonding intermolecular forces, whereas phosphine has dipole-dipole and/or dispersion intermolecular forces. Water also has hydrogen-bonding intermolecular attractive forces. Ammonia is more soluble in water than phosphine because ammonia molecules can hydrogen-bond with water molecules, whereas phosphine molecules cannot hydrogen-bond with water molecules. *When thinking about SOLUBILITY, think about types of forces (likes dissolve likes). For water, H-bonding is most important, so if a compound has H-bonding then it is more soluble than if a substance has dipole forces.
What does a catalyst look like in a reaction?
It goes in as a reactant and comes out as an unharmed product. It does not show up in the FINAL OVERALL reaction.
What does the second order integrated rate law graph look like? Second order equation?
1/[A] = kt + 1/[A]
What is the half life? Equation?
It's the time required for one half of one of the reactants to disappear. t1/2 = 0.693/k for first order
What is the collision theory?
As more collisions in a system occur, there will be more combinations of molecules bouncing into each other. If you have more possible combinations there is a higher chance that the molecules will complete the reaction. The reaction will happen faster which means the rate of that reaction will increase.
What is the Differential Rate Law (Rate Expression)?
It's the RELATIONS BETWEEN RXN RATE AND THE CONCENTRATION of reactants given by a mathematical equation.
Types of orders?
Zero order: The change in concentration of reactant has no effect on rate. (Rate = k) First order: Rate is directly proportional to the reactants concentration. (Rate = k [A] Second order: Rate is quadrupled when reactants concentration is doubled. (Rate = k [A]^2)
How to find the units of the rate constant k?
M^(1-n)s^-1
Explain: Iodine has a greater boiling point than bromine even though the bond energy in bromine is greater than the bond energy in iodine.
Iodine and Bromine are completely covalent molecules that have London Dispersion Forces. Since Iodine is a bigger molecule, it has more e-, and is therefore more polarizable. Since it is more polarizable, it has stronger LDFs than Bromine, leading to a greater boiling point.
Ionization energy increases as you get closer to the nucleus. If you remove an electron from a higher energy level, it will take less energy.
For Na, the first I.E is much lower than the second I.E because the first I.E is taking an electron from the 3rd energy level while the 2nd I.E is taking an electron from the 2nd energy level. (closer to the nucleus)
Account for the bond length of F2 being bigger than the bond length of N2?
The bond length in N2 is less than in F2 because the N-N bond is triple and the F-F is single. Triple bonds are stronger and therefore shorter than single bonds.
What are the 3 requirements of a reaction mechanism?
1. Must be determined by experiment. 2. Must agree with overall stoichiometry, meaning that the elementary steps must make up the overall rate law. 3. Must agree with the experimentally determined rate law, meaning the rate law must have reactants from slow step.
What is a reaction intermediate?
It's produced in one step, but consumed in another.
To find the orders for integrated rate law, plot the 3 different graphs: [A], ln[A], 1/[A] and find the linear data.
RATE OF CHANGE OF A REACTANT IS ALWAYS NEGATIVE. RATE OF CHANGE OF A PRODUCT IS ALWAYS POSITIVE.
Where does the catalyst usually appear?
It usually appears in the rate determining step (slowest step) because their concentration affects the rxn. * Homogeneous catalysts are included in the rate expression if its the same phase as its reactants.
Why does MgF2 have a higher melting point than MgCl2?
MgF2 and MgCl2 are both ionic compounds. Ionic compounds are dominated by charge density. For this comparison, the charges are the same, so the size of the atoms is the deciding factor. Since F- ions are smaller, MgF2 has a stronger force of attraction and therefore a higher melting point. Smaller interionic distances in MgF2 cause stronger distances and higher melting point. *Keep in mind: Attractive forces dissipate with increased distance.
Why does MgCl2 have a higher melting point and greater electrical conductivity of molten state than SiCl4?
MgCl2 is ionic and SiCl4 is a covalent compound. The electrostatic, interionic forces in MgCl2 are much stronger the the Dispersion forces in SiCl4, and lead to a higher melting point. Molten MgCl2 contains mobile ions that conduct electricity whereas molten SiCl4 is molecular and has no conductivity.
Integrated rate law
The data table contains CONCENTRATION and TIME DATA. We used integrated rate data to know how long a reaction must proceed to reach a concentration. The value of k is equal to the absolute value ( I slope I) of the slope of the best fit line which is decided by graphing the 3 linear regressions. Time is on the x axis. Concentration is on the y axis.
Rate = ?
Rate = change in concentration of a species / time interval RATE IS EQUAL TO A CHANGE IN SOME MEASURABLE QUANTITY PER UNIT TIME.
Evaluating the experimental data
1. Look for the two trials where the concentration of a reactant was held constant. 2. Once you have determined the factor by which the concentration of the reactant was changed, determine how that affected the rate for those two trials. *if the rate doubles when the concentration doubles, it's first order. *if the rate quadruples when the concentration doubles, it's second order. *if the rate increases by a factor of eight when the reactant was doubled, it's third order. *if the rate remains constant when the concentration was doubled, it's zero order.
What does the zero order integrated rate law graph look like? Zero order equation?
[A]=-kt + [A0]
What makes a successful collision?
Sufficient energy & correct orientation. *Collisions must occur with enough energy to overcome the electron repulsion of the valence shell electrons of the reacting species and to transform translational energy into vibrational energy to penetrate into each other so that the electrons can rearrange and form new bonds.
What is an order?
It's the exponent on its concentration term in the rate expression. One must analyze concentration and rate data to make this determination. Overall order is the sum of all exponents.
What's the purpose of a catalyst?
It alters the rxn pathway by lowering Ea -> more collisions -> increased rxn rate.
What is the advantage of heterogenous catalysts?
Heterogeneous catalysis offers the advantage that products are readily separated from the catalysis. They are more stable and degrade much slower than homogeneous catalysts.
What is the Maxwell-Boltzmann distribution?
If the temperature is increased, the molecules speed up and collide more frequently. The great majority doesn't have enough energy and will simply bounce apart. THE OVERALL ENERGY OF THE PARTICLES DOES NOT CHANGE MUCH!!! NOTE THAT A MUCH GREATER NUMBER OF PARTICLES HAVE ENOUGH ENERGY TO REACT.
REMEMBER THAT THE RATE EXPRESSION CANNOT BE PREDICTED FROM THE OVERALL STOICHIOMETRY. THE RATE EXPRESSION OF AN ELEMENTARY STEP IS PREDICTED FROM THE STOICHIOMETRY OF THE ELEMENTARY STEP.
How do you determine the value of the rate at a particular instant of time? (INSTANTANEOUS RATE)
Simply compute the slope of a line tangent to the curve at that point in time. (MEMORIZE THIS)
Definition for unimolecular, bimolecular, and termolecular?
Unimolecular involves one reactant molecule that collides with a solvent or background molecule thereby becoming collisionally activated. Bimolecular: Collision between 2 reactant molecules. Termolecular: Collision between 3 reactant molecules.
Differential rate law
The data table contains CONCENTRATION and RATE DATA. You can determine the orders of the reactants and the rate constant using either table logic or ugly algebra.
Ionization energy
Energy required to remove one e-. The removal of 2nd and 3rd e-'s requires more and more energy because the electron:proton ratio is decreasing (fewer electrons for the positive nucleus to attract, therefore Coulombic attractive forces are increasing and the remaining s electron are more tightly held.`
Why does SbCl3 have a measurable dipole moment, whereas SbCl5 does not?
SbCl3 has a measurable dipole moment because it has a lone pair of e-'s which causes a dipole. The dipoles do not cancel out. SbCl5 has no dipole moment because its dipoles cancel. SbCl3 is a trigonal pyramidal structure and SbCl5 is a trigonal bipyramidal structure.
What do catalysts do in a reaction mechanism?
Catalysts alter the mechanism so the activation energy barrier can be lowered, thus speeding up the reaction by offering a different pathway for the reaction. THE OVERALL CHANGE IN ENERGY IS NOT CHANGED FOR THE PROCESS, BUT THE ACTIVATION ENERGY IS LOWERED.
What is a reaction mechanism?
This mechanism represents the sequence of bond making and bond breaking steps that occurs during the conversion of reactants to products.
Explain: At 25ºC and 1 atm, F2 is a gas and I2 is a solid.
If F2 is a gas at R.T and I2 is a solid at T.T, this indicates that F2 has weaker dispersion forces than I2 because it has already passed its boiling point to become a gas whereas I2 is still a solid (has not gone through m.p) I2 is bigger so higher mass (and more e-'s) so larger LDFs.
What does the differential rate law zero order graph look like?
Half life decreases with decreasing concentration.
How do you determine the differential rate law expression?
You must conduct experiments.
How do you calculate the value of the rate constant k?
YOU NEED TO HAVE 2 THINGS: REACTION ORDER, CONCENTRATION, AND RATE. Rate = k [B]^1 k= Rate/[B]^1
What does the first order integrated rate law graph look like? First order equation?
ln[A]=-kt + ln[A0]
Steps to find the order using graph:
1. List 1 is the time (s). List 2 is the concentrations. List 3 is ln[L2] and List 4 is 1/[L2]. Click Zoom 9 if you can't really define the line. Then change the Y list to L1 vs L2, L1 vs L3, and L1 vs L4. Then to find the slope, click stat and go to calc #4. Adjust the Y list according to the stats u used for the straight line graph.
Explain: The melting point of NaF is 993ºC, whereas the melting point of CsCl is 645ºC.
Both NaF and CsCl are ionic compounds with the same charges on the cations and anions. The ionic radius of Na+ is smaller than the ionic radius of Cs+ and the ionic radius of F− is smaller than the ionic radius of Cl−. Therefore, the ionic centers are closer in NaF than in CsCl. Since the force of attraction is inversely proportional to the distance between the ion centers (Coulomb's Law), the compound with the smaller ions will have the stronger attractions and the higher melting point.
Section 2
(12 cards)