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.
What order of kinetics does half life follow?
first order kinetics
How can the amount of atoms that remain after decay be expressed?
What kind of relationship is this?
What graph would be produced if you plot the logarithm of amount of atoms as a function of time?
At = Aoe^(-kt) or
ln (At/Ao) = -kt
note the rate constant, k, is exponential. Radioactive decay is a type of exponential decay. Plotting the logarithm of amount of atoms as a function of time would produce a straight line semi-log plot.
General rule in working with radioactive decay chemical equations
make sure the atomic number and mass on left and right side are equal
Change in the number of protons lead to a change in the identity of an element. By contrast, an atom that loses or gains neutrons or electrons is still the same element.
Alpha decay
Loss of an alpha particle, He (2 protons and 2 neutrons).
Beta decay
The breakdown of the neutron into a proton and electron, and the expulsion of the newly created electron.
The atomic number increases by one but mass stays the same
Positron emission
A type of beta decay
The emission of a positron where a proton becomes a neutron.
Positron can be thought of as electron with a positive charge. Both electrons and positrons are considered to be beta particles. In positron emission, a proton is transformed into a neutron and a positron is emitted
Electron capture
Capture of an electron and the merging of that electron with a proton to create a neutron. A proton is destroyed and a neutron is created
Gamma ray decay
What is a gamma ray?
When does it occur?
A gamma ray is a high frequency photon. It has no mass or charge, and does not change the identity of the atom from which it is given off. It often accompanies the other types of radioactive decay.
Gamma ray emission can occur when an electron and positron collide. Also in annihilation when matter and antimatter collide. Mass is destroyed and converted to energy in the forms of gamma rays.
Electron affinity
What does it mean when electron affinity is exothermic vs. endothermic?
energy change when an electron is added to an atom
exothermic, negative energy change associated with stronger electron affinity - system doing work, releasing energy
reaction is endothermic when a noble gas accepts an electron.
absorption line spectrum
measures the energy absorbed when the electron moves up to a higher energy state
what’s special about electromagnetic energy
how to transfer energy from one point to another via an electromagnetic wave and how to increase the amount of energy transferred:
According to Einstein, if photon is a particle, what can you infer about the change in energy
it is quantized in discrete units of frequency
If energy is transferred from one point to another via an electromagnetic wave, and we wish to increase the amount of energy transferred, the energy can only change in discrete increments given by change in energy of a photon = h*f
energy is transferred in discrete increments where the change in energy is Planck constant (h) times frequency. If we consider a photon as a discrete particle, then change in energy of a photon can also be h*f
how to explain the wave characteristics of electrons and other moving masses
wavelength is h/mv
what is a rate constant and what is it affected by
The rate constant, k, shows the fraction of collisions with right spatial orientation and energy out of the total collisions that occur.
also includes the effect of temperature and activation energy. temperature increase k and activation energy decrease k
Does pressure, temperature, and catalyst affect the rate constant, k?
YES
what is a rate constant and what is it affected by
proportional to the rate of the reaction; shows the fraction of collisions with right spatial orientation and energy out of the total collisions that occur.
Predicting the overall rate in multi-step reactions: what happens if the fast step is the first step and the slow is next?
intermediate of the first step will reach equilibrium quickly. so we can use the equilibrium concentration of the intermediate to in the rate law to determine the rate of reaction
the intermediate of the first step will be included in the rate law but it’s equilibrium concentration must be considered.
What is the difference between the order of an overall reaction versus the reactants?
How do you find the order of an overall reaction?
order of the reactant specifies how that particular reactant affects the reaction rate over time whereas overall reaction order indicates the general influence of the reactants over time
the overall reaction order is the sum of reactant coefficients whereas the reactant order is the coefficient of the reactant
Does temperature, viscosity, and dielectric constant affect the rate constant of a solvent?
YES
When would a catalyst affect the rate of reaction?
When it does affect the rate of reaction, how does it influence the rate law? And what is the extent of the effect of the original reaction?
when the catalyst concentration is very small
the catalyst reaction rate is added to the original rate of reaction. the rate of the original reaction is negligible though
What does the dielectric of the solvent measure?
What does it mean when the dielectric of a solvent is high versus low?
Solvent’s ability to cancel the solute’s internal charge
Measure of solubility for ionic compound. If high, it indicates that the solvent is likely to be polar. If low, likely to be non-polar.
What is the rate constant of solvent affected by
temperature and dielectric constant
how to determine the kinetic energy of an emitted electron
hv (energy input) - work function (energy needed to eject an electron)
energy input only in discrete units of wave frequency
how to figure out equilibrium constant K
you can use the coefficients from the balanced equation into the law of mass action
depends on the stoichiometry not the mechanism of the reaction
What is the effect of a catalyst on the equilibrium constant?
No effect
Describe a metal - what is special about it?
Size of the atom, the trend of metallic character aross the periodic table
great conductor of electricity, made into sheets and strips, and ductile because it is atoms that lose electrons easily so the large atoms themselves are cations in a sea of electrons
metallic character increase down and left toward Francium
how much is 1 gram in amu?
6.02 X 10^23
electron affinity for noble gases: is it favorable? is it endothermic or exothermic?
endothermic b/c noble gases are already stable so they need energy to add an electron
