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cem 141 215 Questions and CORRECT Answers
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cem 141 215 Questions and CORRECT Answers
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cem 141 215- ANS-electromagnetic spectrum and forms of radiation
- ANS-molecular view of endothermic reaction
- ANS-molecular view of exothermic reactions
- ANS-structural formula steps
- A model of an ideal gas as a collection of point particles in constant motion undergoing
completely elastic collisions
- Gas particles are in continuous, random motion. Collisions between gas particles are
completely elastic. In other words, there is no net loss or gain of kinetic energy when particles
collide. The average kinetic energy is the same for all gases at a given temperature, regardless
of the identity of the gas - ANS-Kinetic molecular theory for gases
- a negatively charged ion - ANS-Anion
- a positively charged ion - ANS-Cation
- Classical mechanics adequately describes the motions of bodies much larger then atoms,
while quantum mechanics describes the motions of subatomic particles and atoms as waves
- Classical Mechanics deals with the motion of objects under forces or their own momentum. ...
Quantum Mechanics deals with the behavior of objects at the microscopic level where matter
and energy start to mathematically converge because both can be observed to have wave-like
behaviors at the level of Planck's constant. - ANS-Difference between classical mechanics and
quantum mechanics
- geometrical arrangement of electron groups
- The geometric arrangement of orbitals containing the shared and unshared electron pairs
surrounding the central atom of a molecule or polyatomic ion. - ANS-Electron Geometry
-a formula giving the proportions of the elements present in a compound but not the actual
numbers or arrangement of atoms.
-a chemical formula showing the ratio of elements in a compound rather than the total number
of atoms - ANS-empirical formula
-Electrons in bonding orbitals stabilize the molecule because they are between the nuclei. They
also have lower energies because they are closer to the nuclei. ... Antibonding orbitals are at
higher energy levels than bonding orbitals
,-Bonding orbitals place most of the electron density between the nuclei of the bonded atoms.
Antibonding orbitals place most of the electron density outside the nuclei. - ANS-Difference
between bonding orbitals and antibonding orbital
-geometrical arrangement of atoms
-Molecular geometry is the three-dimensional arrangement of ATOM in a molecule -
ANS-Molecular Geometry
-if V ↓, the number of collisions with the container walls per second must ↑
-therefore P ↑
-Gases can be compressed because most of the volume of a gas is empty space. If we
compress a gas without changing its temperature, the average kinetic energy of the gas
particles stays the same. There is no change in the speed with which the particles move, but the
container is smaller. Thus, the particles travel from one end of the container to the other in a
shorter period of time. This means that they hit the walls more often. Any increase in the
frequency of collisions with the walls must lead to an increase in the pressure of the gas. Thus,
the pressure of a gas becomes larger as the volume of the gas becomes smaller. - ANS-Explain
Boyle's law in terms of the kinetic molecular theory.
-In chemistry, the standard state of a material (pure substance, mixture or solution) is a
reference point used to calculate its properties under different conditions.
-Standard state conditions are defined by Standard Temperature & Pressure (STP) with a
temperature of 0 oC or 273.15 Kelvin (K) and a pressure of 1 atmosphere (1 atm = 101 325 Pa),
temperature. At STP (Standard Temperature & Pressure) 1 mol of ideal gas occupies 22.4 L.
-Here are the conditions for a standard state set of data
- Gases are at 1 atm
- Solutions are at 1 M
-Temp is usually at 25°C (other temp can be specified)
-Elements or compounds are in their most stable form for the stated temperature
When a ΔH value is under standard state conditions, it is given - ANS-standard state
-Potential Energy is the stored energy in an object or system because of its position or
configuration. Kinetic energy of an object is relative to other moving and stationary objects in its
immediate environment. Potential energy is not relative to the environment of an object.
-Potential energy is the stored energy in an object due of its position or its configuration
whereas Kinetic energy is the energy which a body possesses because of its motion -
ANS-Difference between kinetic and potential energy
-Pressure-volume work (or PV work) occurs when the volume V of a system changes. PV work
is often measured in units of litre-atmospheres where 1L. atm = 101.325J.
-The meaning of work in thermodynamics, and how to calculate work done by the compression
or expansion of a gas.
Key Points:
, Work is the energy required to move something against a force.
The energy of a system can change due to work and other forms of energy transfer such as
heat.
Gases do expansion or compression work following the equation:
work=−PΔV - ANS-pressure volume work
-sp3 -combination of one s-orbital and three p-orbitals •Resultant orbitals are 109.5° apart
•common in four bonded carbon compound
-sp2 - the result of an s-orbital mixing with two p-orbitals •Resultant hybrid orbitals are 120°
apart
sp - sp hybridization is most common in compounds that have linear geometry •often
accompanied by triple bonds or two doubles •A single s and p-orbital are hybridized leaving 2
unhybridized p-orbitalint - ANS-types of hybridization
-the mixing of atomic orbitals to produce a new set of orbitals that have characteristics of the
original orbitals. (only occurs in covalent bonding)
-In chemistry, orbital hybridization (or hybridization) is the concept of mixing atomic orbitals into
new hybrid orbitals (with different energies, shapes, etc., than the component atomic orbitals)
suitable for the pairing of electrons to form chemical bonds in valence bond theory -
ANS-Hybridization and the role of atomic orbitals
-The molar volume, symbol Vm, is the volume occupied by one mole of a substance (chemical
element or chemical compound) at a given temperature and pressure. It is equal to the molar
mass (M) divided by the mass density (ρ).
Density(d)=m/V - ANS-Relationship between molar volume, molar mass and density
-the number of representative particles contained in one mole of a substance; equal to 6.02 x
10^23 particles.
- Avogadro's number is a proportion that relates molar mass on an atomic scale to physical
mass on a human scale. Avogadro's number is defined as the number of elementary particles
(molecules, atoms, compounds, etc.) per mole of a substance. It is equal to 6.022×1023 mol-1
and is expressed as the symbol NA. - ANS-Avogadro's number
-The standard enthalpy of formation is the enthalpy change in the formation of one mole of a
substance in its standard state from elements in their standard form
H2(g)+12O2(g)→H2O(l)ΔHf!=−285.8kJ
-The standard enthalpy of formation is defined as the change in enthalpy when one mole of a
substance in the standard state (1 atm of pressure and 298.15 K) is formed from its pure
elements under the same conditions.
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