Exam 3 – Chemistry Test Questions – Flashcards
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| Single covalent bonds between non-metals are very ______ and take _____ of energy to break; double and triple bonds are even _______ |
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| Strong, lots, stronger |
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| Covalent bonds are ______ than ionic bonds, but individual molecules behave much differently than ionic aggregates |
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| Stronger |
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| The ability of an atom in a molecule to attract the shared electrons in a covalent bond. The attraction of shared electrons by atoms; differences lead to covalent bond polarity and then to ionic character (left to right) |
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| Electronegativity |
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| In polar covalent bonds, the electron density surrounds the most ________ atom since its nucleus has the greater electron attraction |
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| Electronegative |
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| Ionic bonds are _____ but not covalent |
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| Polar |
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| Small atoms with _____ effective nuclear charge have ______ electronegativity |
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| High, highest |
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| Large atoms with _____ effective nuclear charge have ________ electronegativity |
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| Low, lowest |
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| A representation of an atom's valence electrons by using dots and indicates by the placement of dots how the valence electrons are distributed in the molecule. The 4 sides of an atomic symbol are surrounded by its number of valence electrons, first singly, then doubly. A single covalent bond represents the sharing of single valence electrons between two atoms |
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| Electron-dot Structures (Lewis Structures) |
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| The number of valence electrons is equal to the |
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| Group number |
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| The choice of single, double, or triple is to be sure each atom shares or owns a(n) ______ of electrons |
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| Octet |
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| _____ one valence electron for each negative charge and _______ one valence electron for each positive charge |
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| Add, Subtract |
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| 8 - the group number (number of valence electrons) = |
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| The number of bonds needed |
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| The central atom of a Lewis Dot Structure is the most |
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| Electronegative atom |
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| Atoms with _______ can have more than an octet |
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| d-orbitals |
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| Structures that differ only in the movement of electrons are |
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| Resonance Structures |
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| Electrons in bonds and in lone pairs can be thought of as "charge clouds" that repel one another and stay as far apart as possible, this causing molecules to assume specific shapes. Working from an electron-dot structure, count the number of "charge clouds" and the determine the molecular shape |
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| VSEPR (Valence Shell Electron Pair Repulsion Model) |
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| For a central atom with two electron clouds, VSEPR predicts a _____ shape with a bond angle of _____ |
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| Linear, 180 degrees |
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| For a central atom with three electron clouds, VSEPR predicts a _________ shape with a bond angle of ______ and molecular shape of ______ |
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| Trigonal planar, 120 degrees, bent |
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| For a central atom with four electron clouds, VSEPR predicts a ________ shape with a bond angle of ______ |
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| Tetrahedral, 109.5 degrees |
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| For a central atom with four electron pairs, if one bond is replaced with a lone electron pair, the molecule is ________ |
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| Trigonal pyramidal |
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| For a central atom with four electron clouds, if two bonds are replaced with two lone pairs, the molecule is ______ |
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| Bent |
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| For expanded octets with five bonds, the VSEPR model predicts ____________ with bond angles of _______ and _______ |
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| Trigonal bipyramidal, 90 degrees, 120 degrees |
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| For a central atom with five electron clouds, if one electron bond is replaced with a lone electron pair, then it is a ________ molecule |
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| Seesaw |
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| For a central atom with five electron pairs, if two bonds are replaced with two lone electron pairs, then it is a ________ molecule |
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| T-shaped |
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| For a central atom with five electron pairs, if three bonds are replaced with three lone electron pairs, then it is a ______ molecule |
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| Linear |
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| For a central atom with six electron pairs, the VSEPR model is _________ with a bond angle of |
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| Regular octahedron, 90 degrees |
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| For a central atom with six electron clouds, if one bond is replaced with one lone electron pair, the it is a _______ molecule |
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| Square Pyramidal |
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| For a central atom with six electron clouds, if two bonds are replaced with two lone electron pairs, it is a _________ molecule |
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| Square planar |
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| A quantum mechanical model which shows how electron pairs are shared in a covalent bond. The covalent bond results from overlap of valence atomic orbitals (s-s and p-p overlap) |
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| Valence Bond Theory |
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| Each overlapping orbital has one electron or opposite spin. The orbitals maintain their shape (spherical for s and lobed for p). Covalent bonds are formed by overlap of atomic orbitals, each of which contains one electron of opposite sign. Each of the bonded atoms maintains its own atomic orbitals, but the electron pair in the overlapping orbitals is shared by both atoms. The greater the amount of overlap, the stronger the bond |
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| Valence Bond Theory |
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| Overlap of s and p orbitals cannot explain the symmetry of molecules in VSEPR so new orbitals called __________ are created |
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| Hybrid orbitals |
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| When two sp^2 atoms form a double bond, overlap of sp^2 orbitals form a single bond, called _______, and overlap of the p-orbitals give a ______ bond |
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| Sigma, pi |
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| The capacity to supply heat or do work |
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| Energy |
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| The energy of motion |
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| Kinetic energy |
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| Stored energy |
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| Potential energy |
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| Energy cannot be created or destroyed; it can only be converted from one form to another |
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| Law of Conservation of Energy |
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| The kinetic energy of molecular motion and is measured by finding the temperature of an object. Molecular motion provides this |
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| Thermal energy |
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| The amount of thermal energy transferred from one object to another as the result of a temperature difference between the two |
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| Heat (q) |
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| The total internal energy of an isolated system is constant. Total energy is equal to the final energy minus the initial energy |
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| First Law of Thermodynamics |
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| Energy can be treated like a reagent; if delta U is _______ then starting material (energy absorbed or if delta U is ______ then the product (energy released) |
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| Positive, negative |
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| A function or property whose value depends only on the present state, or condition, of the system, not on the path used to arrive at that state. Energy is an example of this, meaning that the chemical energy content is independent of how the chemical is made |
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| State Function |
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| Chemical energy (U) can be used to do ______ (Force * Distance) |
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| Work |
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| With combustion, the increase in gas volume __________ the volume under the piston, pushing it _______ |
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| Expands, upward |
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| Work done as the result of a volume changed in the system. Also called pressure-volume or PV work |
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| Expansion work |
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| Changes in chemical energy are best measured as _________ at constant pressure |
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| Heat flow (q) |
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| A state function whose value depends only on the current state of the system, not on the path taken to arrive at that state. The heat content at constant pressure; Change in this is measured as heat flow during a reaction |
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| Enthalpy |
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| Most stable form of a substance at 1 atm pressure and at a specified temperature, usually 25 degrees C for all substances in solution |
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| Thermodynamic Standard State |
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| The amount of heart necessary to melt a substance without changing its temperature (melting) |
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| Enthalpy of Fusion |
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| The amount of heat required to vaporize a substance without changing its temperature (boiling) |
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| Enthalpy of Vaporization |
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| The amount of heat required to convert a substance from a solid to a gas without going through the liquid phase (solid to gas) |
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| Enthalpy of Sublimation |
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| Reactions that release heat are called _________ |
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| Exothermice |
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| Reactions that gain heat are called ________ |
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| Endothermic |
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| The amount of heat required to raise the temperature of an object or substance a given amount |
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| Heat capacity (C) |
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| The amount of heat required to raise the temperature of one mol of a substance by one degree C |
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| Molar Heat Capacity |
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| The amount of heat required to raise the temperature of one gram of a substance by one degree C |
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| Specific Heat |
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| Liquids hold _______ heat relative to solids as molecular motion (molecules in liquids are free to move) |
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| Much more |
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| The overall enthalpy change for a reaction is equal to the sum of enthalpy changes for the individual steps in the reaction |
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| Hess's Law |
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| The enthalpy change for the formation of one mol of a substance in its standard state from its constituent elements in their standard states |
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| Standard Heat of Formation |
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| Standard Heat of Formation are used to calculate _________ for a reaction of those substances; Standard heat of formation values must be multiplied times their stoichiometry and reactants are subtracted from their products |
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| Enthalpy change |
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| Standard enthalpy changes for the corresponding bond-breaking reactions |
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| Bond dissociation energies |
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| A substance where particles are far separated relative to their volume; particles do not interact |
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| Gas |
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| Motion of particles of a gas is dependent of _________ |
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| The temperature |
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| Collision of gas particles are |
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| Elastic |
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| Particles in constant motion, colliding with the container |
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| Pressure |
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| Measured with a barometer; Hg is used because of its high density |
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| Atmospheric pressure |
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| Measures pressure differences between two systems, one typically atmosphere |
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| Manometer |
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| A gas whose behavior follows the gas laws exactly |
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| Ideal gas |
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| Showed that Pressure*Volume changes are linear only with Pressure versus 1/Volume at constant mols (n) and temperature (K). Decrease in volume, increase in collisions and pressure |
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| Boyle's Law |
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| Showed that Volume and Temperature are directly proportional at constant n and Pressure. Increase in temperature increases collisions so volume must expand to reduce collisions, maintaining a constant pressure |
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| Charles' Law |
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| Showed that Volume and mols are directly proportional at constant temperature and pressure. More particles means more collisions, the volume expands to reduce collisions, maintaining constant pressure |
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| Avogadro's Law |
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| At standard temperature and pressure of gases (STP), the volumes of all gases are the same, even for mixtures of gases and the volume is |
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| 22.414 Liters |
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| The total pressure exerted by a mixture of gases in a container at constant Volume and Temperature is equal to the sum of the pressures of each individual gas in the container |
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| Dalton's Law of Partial Pressures |
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| A gas consists of tiny particles, either atoms or molecules, moving about at random The volume of the particles themselves is negligible compared with the total volume of the gas; most of the volume of a gas is empty space The gas particles act independently of one another; there are no attractive or repulsive forces between particles Collisions of the gas particles, either with other particles or with the walls of a container, are elastic (constant temperature). They do not lose energy The average kinetic energy of the gas particles is proportional to the Kelvin temperature of the sample |
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| The Kinetic-Molecular Theory of gases |
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| The velocity of gas particles depends on _______, average speed decreases with increase in size |
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| Particle size |
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| Speed obeys a __________ about a mean; as temperature increases, the distribution is more spread out |
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| Gaussian distribution |
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| The mixing of different gases by molecular motion with frequent molecular collisions |
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| Diffusion |
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| Gas molecules will ______ until the distribution of gases is equal; the rate is inversely proportional to the molar mass |
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| Diffusion |
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| The escape of a gas through a pinhole into a vacuum without molecular collisions |
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| Effusion |
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| Real gases do not obey ______; they form at high concentration of gas molecules, this increases ideal volume |
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| Ideal Gas Law |
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| Concentration in real gases also allows molecular interaction; typically attraction, which reduces ideal pressure. Attractive forces between particles become __________ at higher pressures |
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| More important |
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