Chapter 5: Thermodynamics

A hot object is placed next to a cold object so that they are touching. Which of the following statements is true? I. Heat will transfer from the hot object to the cold object because the hot object has a higher temperature. II. The two objects are in thermal equilibrium III. Internal energy will transfer from the hot object to the cold object because the hot object has greater internal energy. (a) I (b) II (c) I & III (d) III

a

∆Hcomb

product-reactant

-path independent -depends only on the current state of a system -depends only on the difference between the initial and final states

state function

What happens when a bond is broken?

takes energy (+)

the energy needed to break 1 mole of covalent bonds in the gas phase

bond energy

finding (bond energies) ∆H°rxn or ∆Hf°

reactant-product

Atmospheric gases absorb more energy than they emit. If we consider a gas to be a closed system, which of the following is true? (a)the heat absorbed by the gas is positive (b)the internal energy of the gas increases (c)the change in volume of the gas is negative (d)the work done on the gas is equal to the change in internal energy and the heat absorbed by the gas

a

Additional gas is pumped inside a rigid container that stores compressed gas. Which of the following is a true statement about this system? (a)pressure is constant throughout the compression (b)there is no work done on the container (c)the molar concentration of gas is decreasing (d)the volume of the container is decreasing

b

Which of the following scenarios violates the first law of thermodynamics, "the conservation of energy?" (a)a spring that extends and retracts forever, alternating between potential and kinetic energy (b)An isolated electrochemical cell that indefinitely generates an electrical current (c)an efficient wind turbine that converts all of its energy from mechanical movement into electrical potential energy (d)a machine that converts heat energy into work energy

b

Equal amounts of heat are absorbed by 100 g samples of various solid metals with differing specific heat values. Which of the following statements is true regarding metals and their specific heat values? (a)the metal with the smallest specific heat will undergo the smallest change in temperature (b)the metal with the smallest specific heat will resist melting to a greater degree at its melting point (c)the metal with the greatest specific heat will undergo the smallest change in temperature (d)the metal with the greatest specific heat will resist melting to a greater degree at its melting point

c

When heating a solution, a scientist detects a temperature increase in the solution during a period of time. Which of the following statements accurately characterizes the solution during this period? (a)The solution is at boiling point (b)The solution is undergoing a phase change (c)the velocity of molecules in the solution is increasing (d)the solution's temperature increase is proportional to its ∆Hvap

c

Which of the following statements is true concerning a chemical reaction? (a)Endothermic reactions have lower activation energies than exothermic reactions (b)Exothermic reactions are always spontaneous (c)The ΔH value for the forward reaction is negative the ΔH value of the reverse reaction d)A catalyst reduces the enthalpy change for the reaction

c

In a system undergoing adiabatic compression, what are the values of internal energy and heat if work done on the system is 500 \text{ J}500 J? (a)internal energy is 0J and heat is 500J (b)internal energy is -500J and heat is 0J (c) internal energy is 0J and heat is -500J (d)Internal energy is 500 J and heat is 0 J

d

if ∆Hrxn>0 then the reaction is _________and heat is _________

endothermic, absorbed

A positive value for ∆H means that energy in the form of heat is ____________ the system from the surroundings

entering

A negative value for ∆H means that energy in the form of heat is ____________ the system and going into the surroundings

exiting

if ∆Hrxn < 0 then the reaction is ________and heat is ________

exothermic, released

as kinetic energy increases, temperature __________

increases

as temperature increases, kinetic energy __________

increases

_________-->break bonds-->________-->form new bonds--> ________

reactants, atoms, products

What happens when a bond is formed?

releases energy (-)