States of Matter
What is volatility?
Ability of a liquid to transition into a gas
What is the difference between endothermic and exothermic reactions?
Endothermic: heat is absorbed by the system (enters!)
Exothermic: heat is released from the system (exits!)
Explain what occurs at the particulate level throughout a horizontal portion of a heating curve. (hint: think average kinetic energy/temperature)
Temperature and average kinetic energy remain constant; heat energy is being used to break IMFs
Which of the 4 types of solids are conductive (and if applicable, under what conditions?)
Ionic (liquid & aqueous phases only) and metallic
A pot of water begins to boil, forming water vapor. Is this process endothermic or exothermic and WHY?
Endothermic; energy is needed to overcome the IMFs present so the system absorbs heat
Define change in enthalpy.
Amount of heat absorbed or released by a system
Define the following terms:
- Triple point
- Critical point
- Normal melting & boiling points
Triple point: point at which a substance exists in all three states of matter simultaneously
Critical point: point at which liquid and gas are no longer distinguishable
Normal melting & boiling points: points at which substance changes phases at standard pressure
An 800C block of iron is submerged in a glass of 500C water. Estimate the final temperature of each substance.
65oC for both the iron and the water; they eventually reach thermal equilibrium!!
What is the difference between molar heat of fusion and molar heat of vaporization?
Molar heat of fusion: energy needed for phase change between solid and liquid states
Molar heat of vaporization: energy needed for phase change between liquid and gas states
Where are the following values located on a potential energy diagram?
-Transition state
-Activation energy
-Change in enthalpy of reaction
Transition state: highest point on diagram
Activation energy: difference between energy of reactants and transition state
Change in enthalpy of reaction: difference between energy of reactants and energy of products
Substance A has LDFs and dipole-dipole forces. Substance B has LDFs. Which substance has a lower vapor pressure and WHY?
Substance A; has stronger IMFs
What occurs at the particulate level when a system reaches thermal equilibrium? Answer in terms of particle motion and kinetic energy.
The particles have the same average kinetic energy (same temperature!) and remain in motion as they continue to collide
Do phase changes occur during the slanted or horizontal portions of a heating/cooling curve?
Horizontal
What does a potential energy diagram look like for an endothermic reaction vs. an exothermic reaction?
Endothermic: reactant energy is lower; product energy is higher
Exothermic: reactant energy is higher; product energy is lower
Which substance has a higher boiling point: CH4 or SO2? (hint: think IMFs)
SO2
A 17.0 g block of iron absorbs 313.65 J of energy when it is heated from 52oC to 93oC. Determine the specific heat capacity of iron WITH UNITS.
0.45 J/(goC)
Calculate the amount of heat in kJ needed for a 25.0 g sample of liquid water at 45.0oC to heat up to its boiling point of 100.oC and then evaporate completely. (hint: think of slanted and horizontal components of heating curve)
cwater = 4.18 J/(goC)
Molar heat of fusion: 6.01 kJ/mol
Molar heat of vaporization: 40.7 kJ/mol
62.2 kJ
Given the reaction below, calculate the amount of energy released in kJ when 8.00 g of CO2 is produced. The change in enthalpy per mole of reaction is -4327 kJ/molrxn.
C2H8 + 4O2 --> 2CO2 + 4H2O
-393 kJ