CHEM 151 1st Edition Lecture 4Temperature vs. Pressure- Pressure increases as temperature increases because:o The number of collisions in a system increases because particles are moving faster (due to the increased temperature) and collide more frequently with the walls of the container, therefore pressure increases- Pressure: Number of collisions at a given time (defined by particulate model of matter)- As temperature increaseso Average kinetic energy of the system increaseso Average velocity increaseso Number of collisions increaseo Higher pressure- Increasing particle: More particles will collide more frequently and therefore increases pressure- Behavior is the same for all gases. Particles are very far away from one another so they have less interactionsIdeal Gas Law- The particulate model of matter predicts a relationship of the following type for gases at high temperature and low pressureo P=kB (NT / V )o Proportionally constant: kB=1.380 x 10-23 J/K Known as Boltzmann constanto None of the quantities in this relationship depends on the chemical composition of the actual systemIntermolecular Forces (IMF)- Without interparticle interactions there are no phase changes- When repulsive interactions are increased- molecules repel each other, then bounce off the system walls and pressure will increase- When attractive forces are increased- molecules will stick together and pressure will decrease due to less frequent collisions Phase Change- To stimulate phase changeo Decrease temperature to make a solid from gas o Increase pressure by decreasing the volume This forces particles into smaller regions of spaceModeling Phase Transitions- To explain the existence of phase transitions we have to assume that there are intermolecular forces among particleso IMF allow us to explain phase changes- When temperature decreases, the average kinetic energy per particle decreaseso Attractive forces between particles are then able to hold them together- During a phase changeo Force strength and size of particles do not changeo How particles are distributed and spaced are what’s changingo Amount of energy particles have changesKinetic vs. Potential Energy- Attractive and repulsive interactions between particles change their kinetic and potential energies- Potential energy: stored energy, the possibility of movement- Kinetic energy: The energy of motiono Influenced by temperature- The farther apart the molecules are, the more positive potential energy they have- The closer the molecules are, the more negative potential energy they haveo Less potential energy as they move closer (more negative potential energy) the less stability and favorability-Potential energy is a measure of the kinetic energy that could potentially be gained. Thus, it decreases as particles move towards each otherPotential Energy- Particles that attract each other are said to have negative potential energy compared to free particleso By convention, there is more negative potential energy the closer the molecules are together, and vise versa- Repulsiono Atoms physically cannot occupy the same spaceo They can be so close that they repel each other (this is a pretty genericforce)Potential vs. Kinetic Energy- During a phase transition all the energy is invested or lost in the form of potential energy- The average kinetic energy per particle does not change during a phase change if temperature does not change- To separate molecules, you must invest potential energy- To bring molecules closer together, you extract that potential energy- Constant temperature = constant kinetic energy- Kinetic energy is constant during phase changeo It increases after the phase change- If energy is positive- it’s being absorbed- If energy is negative, it’s being releasedo Liquid -> solid: energy is being released, therefore energy is negativeo Solid -> liquid: energy is being absorbed, therefore energy is positive- Potential energy is a function of distance and attractive forcesExplaining Change- Building explanations and making predictions about the phase changes that asystem may undergo can be simplified by analyzing two critical elementso The potential energy of the different states available to the system Different states of matter have different potential energieso The number of configurations that particles can take in each of those states Focuses on the randomness of the systemLiquid <-> Gas- Gas is more randomo Particles touch to a much less extent- Increasing the temperature = increasing potential energy- Increasing the pressure = less number of configurations- Randomness results in a larger number of configurations- PEC diagramo Increase potential energy by increasing temperature or increasing pressureo **Potential energy doesn’t influence number of configurationsStability- Something is more favored when it is more stable- therefore having a lower potential energy- Configurationally, something that is more stable is more random, because randomness is favoredo EX: If a teacher assigns seats in a classroom, that is not random. It takes a lot more energy for the teacher to ensure that every student sits in his or her assigned seat. Conversely, if seats are random and students sit where they please, this requires no energy on the teacherspart, and is therefore favored- Randomness is also favored because there are more possibilities for numbersof configurations- If a substance has a higher potential energy, it also has a higher boiling