final exam Flashcards
why do most chemical reactions involve heat?
because breaking bonds required energy and forming bonds releases energy, (and heat is energy)
what is and endothermic reaction? an exothermic reaction
endothermic reaction- a reaction in which energy is overall required or absorbed
exothermic reaction- a reaction in which energy is overall released
what is entropy?
disorder
what is a spontaneous reaction?
a reaction that occurs without any continuous outside intervention
2AB2 (g)—>A2 (g) + 2B2 (g)
ΔH is either positive or negative 117 kj/mol for this reaction. which is the correct value. explain?
+117 kj/mol; because it is a decomposition reaction and those are endothermic
2AB2 (g)—>A2 (g) + 2B2 (g)
rewrite the equation as a thermochemical equation with either a positive or negative ΔH
2AB2 (g) + 117 kj/mol—>A2 (g) + 2B2 (g)
2AB2 (g)—>A2 (g) + 2B2 (g)
ΔS is either positive or negative .080 kj/mol K for this reaction. which is the correct value? explain?
+.080 kj/mol; because there is more disorder on the product side that the reactant side, so more minus less would equal a positive entropy
some reactions are always spontaneous and some reactions are never spontaneous. however, some reactions that are no spontaneous can be made spontaneous. how?
some reactions that are no spontaneous can be made spontaneous when in an environment with a different temperature that can make it spontaneous (such as how ice will not melt in a cold environment, but it will melt in a warm/room temperature environment)
gases have a very low density. what assumption in the kinetic molecular theory of gases explains why?
gases particles are separated by large distances, so they have a low density
gases are fluids. what does this mean? explain why gases have this property in terms of the kinetic molecular theory?
gases being fluids means that they flow; the particles of a gas are in constant random motion and they don’t have strong attractive forces
what is pressure caused by
collisions of particles
what happens to atmospheric pressure as altitude increases?
as altitude increases, atmospheric pressure decreases
why are gases not ideal? (give two reasons)
because their particles take up space and they exhibit slight attractive forces
under what conditions of temperature and pressure do real gases most closely have have as ideal gases?
to make a gas closer to an ideal gas, the temperature must be high and the pressure must be low
gay-lussac’s law examines the relationship between pressure and temperature at constant volume. what happens to the pressure of a gas if the temperature increases? explain
when temperature increases, pressure increases because the gas particles will have more energy and hit the sides of the container more often
if the temperature is constant and the volume of a gas decreases, what happens to the pressure? explain
if the volume of a gas decreases, the pressure increases because the gas particles will have less room to move in and will hit the container more often
hot air balloons rise. a balloon filled with helium also rises. explain each
a hot air balloon rises because it is full with gas and as the temperature increases, the volume increases; a balloon with helium rises because helium is a gas with a smaller molar mass. do a gas to lift an object, it has to have a small density, which can be achieved by heating the gas and selecting one with a smaller molar mass
you are given 1 mole of helium gas and an identical container of 1 mole of oxygen gas. both gases are at STP. determine whether each of the following statements are true or false
a. both are ideal gases
b. both gas samples have the same kinetic energy
c. both gases have the same mass
d. both gas particles have the same number of particles
e. both gas samples have the same density
a. false
b. true
c. false
d. true
e. false
list the types of intermolecular forces from strongest to weakest
hydrogen bonds
dipole-dipole forces
london dispersion forces
what is the key difference between a dipole-dipole force and a dispersion force?
dipole-dipole forces result from permanent dipoles, whereas dispersion forces result from temporary dipoles
why do liquids, but not solids, take the shape of their containers?
solids have such strong intermolecular forces that make the particles tightly packed, so they have a definitive shape and volume
of the three states of matter, explain which have a definite volume, explain why each state has or does not have a definite volume
liquid and solid have definite volume. liquids have a definite volume because their intermolecular forces are so strong that particles cannot separate; solids have a definite volume because their intermolecular forces are strong and make their particles tightly packed; gases do not have a definite volume because their particles have weak intermolecular forces (and loosely packed particles)
what is the difference between a crystalline and an amorphous solid? what is true of the melting point of each type of solid?
crystalline solids have particles with highly organized, repeating patterns, but amorphous solids have particles with no repeating patterns and are randomly organized; along with that, amorphous solids soften before they melt and have a (wide) range of temperatures where they experience melting, but crystalline solids have a definite melting point (and do no soften)
what happens to a substance’s kinetic energy as it boils? its potential energy?
a substance’s KE remains constant as it boils (because temp is constant), and its PE increases (because liquid is turning to gas, which gives the particles more freedom to move)
