Introduction to General Chemistry Flashcards
What is a strong nuclear force?
force that holds the protons and neutrons together
What does the binding energy indicate? What does it measure?
It indicates the stability of nucleus
measures the energy needed to break the nucleus into individual protons and neutrons
What is an effective charge?
What is its trend across the periodic table?
the net positive charge felt by the valence electrons or recently added electrons
Increases to the right and down toward Rn, Zeff the RN
What is the difference between complete shielding and no-shielding?
what will be the Zeff for complete shielding and no shielding
electron added feeling a full charge of protons or no charge of protons
Zeff will be 1ev in complete shielding (feels only itself)
Zeff will be Z for each electron
How does the Zeff pattern change after noble gas on the next row? How does Zeff of Na compare to the one directly above it on the periodic table?
There is an added shell so Zeff decreases from noble gas down the row (next alkaline metal)
But Na still has higher Zeff than Li which is directly above it
What is an Electrostatic force
force between charged objects whether it’s attraction, or repulsion.
What is the equation that measures the electrostatic force between charged objects?
How can you find the electrostatic force between the proton and the outermost electron using this equation?
Coulomb’s law
kq1q2/r^2 = F
Plug in Zeff not Z for q1 in Coulomb’s law
Ionization energy: what is it and what’s the trend?
up to the right toward Fluorine
energy needed to detach an electron from an atom
first ionization vs. second ionization and so forth.
what takes more energy? and why?
second. b/c effective nuclear charge increases for the remaining electrons
Describe the photoelectric effect.
How can the kinetic energy of the electron being ejected increase?
One-on-one photon to electron collision. In this one-on-one collision, the photon must have the right quantized energy, the right frequency.Increasing the number of photons will not increase the intensity to bump the electron up.
KE of electron increases only if the frequency of the photon colliding with the electron increases
What is the Minimum energy required to eject an electron called?
the work function aka minimum threshold energy
KE of the ejected electron is given by the energy of the photon (hf) minus the work function
Bond dissociation energy
Higher bond dissociation energy indicates what type of stability?
the energy needed to break the bond
High bond dissociation energy indicates that the bond is very stable
Dipole moment equation
dipole moment = q (charge at the either end of the dipole) - distance (between the centers of charge)
What is avogadro’s number?
How did Avogadro come up with this number?
1 gram is equal to how much amu?
- 02 X 10^23 carbon atoms in 12 grams of 12C
6. 02 X 10^23 amu = 1 gram
How to define “k”, the rate constant? In other words, what are the factors that affect the rate constant?
collision frequency, z
fraction of collisions having the effective spatial orientation, p (steric factor)
fraction of collisions having sufficient relative energy
(e^-Ea/RT) . Note: increase in Ea decrease k (negative exponent)
Do pressure, catalysts, and temperature affect the value of the rate constant?
Yes but pressure is typically relevant only for gases, for which higher pressure increases the rate constant
Catalysts lower the activation energy, increasing the rate constant
temperature: increases more collisions with sufficient kinetic energy (increase both z and p)
What does increasing the rate of a reaction tell you about equilibrium?
it says nothing about the equilibrium. It just means that the rate of forward and reverse reactions are achieved more quickly (achieve equilibrium more quickly)
Is Zero order reaction dependent on the concentration of the reactant?
How does the reaction rate (change in concentration over time) change in a zero order reaction? How is the slope of the graph (change in concentration vs. time) related to k?
What is an example of an enzyme-catalyzed reaction in which zero-order reaction would occur?
What is the rate of a zero-order reaction?
The reaction rate is independent of the concentration of any reactant. So increasing or decreasing the concentration of the reactants has no effect on the rate of the reaction.
The reaction rate (change in concentration) over time is constant. The slope of the graph reaction rate vs. time is zero where y = k. In a graph, concentration over time, the decrease in concentration of reactant is constant where slope is correlated to -k.
This occurs in enzyme-catalyzed reactions when the concentration of the substrate far outweighs the concentration of the enzyme so all the enzyme sites get saturated and adding more substrate has no effect.
The rate of a zero-order reaction is equal to constant k (This rate does not change)
In a first-order reaction, how does the reaction rate change (change in concentration) change over time?
Is the First-order reaction dependent on the concentration of the reactant?
Describe the graphs (reaction rate vs. time) and (ln [A] vs. time) and their relation to k, the rate constant.
Example of a situation in which the first-order reaction would occur?
The reaction rate (change in concentration over time) changes linearly over time.
The reaction rate is dependent on the concentration of reactants.
The concentration of reactants decrease exponentially so [A] vs t is a downward curve approaching zero. ln[A] vs. t, on the other hand, is a straight negative line where the slope is -k, the rate constant.
Radioactive decay
In a multistep reaction, how do you figure out the rate of a reaction when the first reaction is slow? What if the slow step occurs after the first step?
if the first reaction is slow, then the coefficients can be used to derive the rate law.
If the slow step is after the fast step, it can be assumed that the equilibrium of the first reaction is reached very quickly. So you can use the equilibrium concentration of the intermediate in the rate equation of the slow reaction
In what shape of the curve, does the catalyst increase the rate of reaction?
How does a catalyst increase the rate of reaction
exponentially
lower the activation energy and increase the steric factor (put the reactants in favorable orientation for reaction to occur)
creates a different energy pathway increasing the rate of both forward and reverse reactions; may create an intermediate
In what situation, can the concentration of a catalyst be found in the rate law?
In this situation, how would it be represented?
Would it need a separate rate constant, k?
Yes, when the concentration of catalyst is so small that increasing its concentration can increase the rate.
The total rate is given by the sum of the rates of both reactions. Typically, the rate of the original reaction is negligible compared to the rate of the catalyzed reaction.
In this case, reactions with catalysts require separate rate constants.
How does the dielectric of the solvent affect the rate constant, k?
The dielectric constant affects the degree of solvation which affects the rate constant. When a reactant is trapped through the “cage effect”, the solvent electrically insulate the reactant, reducing the electrostatic forces between them. This can decrease the rate constant.
What is radioactive decay?
What atoms are subject to radioactive decay?
What does it mean when an atom is considered “radioactive”?
spontaneous breaking of the nucleus. All atoms other than hydrogen are subject to some type of spontaneous decay.
Being radioactive means that the atom has a relatively high decay rate.