The activities are designed to help students order their thoughts, with discussion and questions playing a part. The subscript "tot" refers to the sum of kinetic and potential energies over all particles. Children will develop their working scientifically skills by: The activity can be used as a model for whole class teaching on the differences between solids, liquids and gases and how they behave. If the mass of Ai is nine times the mass of Cy, calculate the ratio of their speeds at T=500K. The difference between solids, liquids and gases can be explained using the particle model. C1.1 How has the earth's atmosphere changed over time, and why? Generally, a polyatomic gas is composed of molecules having N number of atoms. By considering the polarity and number of electrons present in molecules, it is possible…, C1.1a describe the main features of the particle model in terms of states of matter and change of state, 4.2 Bonding, structure and the properties of matter, 4.2.2 How bonding and structure are related to the properties of substances. Figure 3.5.1: Model of thermal energy with particles attached to springs. This is precisely how we defined thermal energy in Equation 1.2.6 in Chapter 1: except now we add the "V" subscript for accuracy. If we add some energy to the two-particle system without breaking the bond, the bond energy does not change, so only thermal energy changes. In a simple monatomic gas, composed of single atoms, such as He or Ne gases, aka Noble gases, the atoms are no longer interacting with a pair-wise potential since their average separations are \(r\sim 10\sigma\). Read our policy. Another way this molecule can have kinetic energy is through rotations. When energy is added, it is not possible to increase kinetic energy without increasing potential energy. It is the responsibility of the teacher to carry out appropriate risk assessments for the demonstrations. Give each pair a full set of Particle cards. To answer how many ways does each particle in a solid have to have energy, we saw that there are three springs and two modes per spring, so a solid must be six number of modes, 3 KEvib modes and 3 PEvib. 3. When students have completed their sheets, ask them to: Act as advocate for their partner’s success. The total number of modes is the total number of particles N times the number of modes per particle. Translational modes are always active, as long as the temperature is above zero Kelvin. Frozen modes cannot share thermal energy among other modes. explore the use of models to describe gases, liquids and solids. b) You add enough energy to break all weaker bonds. We can find the average speed of a gas particle by considering that each of the three KEtrans modes has \(\frac{1}{2}k_BT\) of thermal energy. Thus, both will have the same magnitude of change in thermal energy. In the previous section we modeled the macroscopic definition of bond energy from Chapter 1 with the microscopic perspective of neutral subatomic particles interacting with a pair-wise potential. The double lines represent strong Ai-Cy bonds, where the single lines are weaker AiCy-AiCy bonds. The particle model for solids, liquids and gases is a controversial topic in science education. the difference between solids, liquids and gases can be explained using the particle model. Students think about gases, liquids and solids in terms of the particle model. This data tells us that not all modes are active at all temperature. Assume there are no phase changes for either substance. They interpret diagrams on cards showing representations of particles and may observe a teacher demonstration. Invite students to describe what they see. The total number modes is the number of particles times the number of modes per particle, so for the solid we get: \[\text{total # modes} = 10N_A\times 6 = 60N_A\nonumber\], \[\text{total # modes} = 60N_A = 12N_A\text{( # modes per particle)}\nonumber\]. Thus, Cy atoms are on average moving three times faster than Ai atoms. 2) Since the two substances are a closed system, \(\Delta E_{\text{thermal}}\) gained by one substance must equal be \(\Delta E_{\text{thermal}}\) lost by the other: \[\text{(total # modes of solid )}|\Delta T_{solid}| = \text{(total # modes of gas)}|\Delta T_{gas}|\nonumber\]. We also discussed the idea of added energy being split evenly between kinetic and potential energies, which will bring us to the idea of Equipartition of Energy below. 3 ways to teach 14–16 students how to apply their knowledge to new scenarios and prepare them for exams, You’ll be hooked on these approaches to improving the quality of student work, Secondary school teacher Ian Stuart shares the benefits of teaching atomic theory to seven- and eight-year olds. There is further information about safety on the demonstration sheet. Substances are made up of tiny particles. That is, there will be about as much energy associated with the random energies of a small piece of the sample as in any other same size small piece. Reinforce their understanding of the terms gas, liquid and solid. Thus each molecule has 3 translational kinetic energy modes. This is known as Equipartition of Energy. They interpret diagrams on cards showing representations of particles and may observe a teacher demonstration. Heat, cool and compress atoms and molecules and watch as they change between solid, liquid and gas phases. The expression above is the macroscopic definition of thermal energy at constant volume. Peer advocacy acts as a further stimulus to encourage learning and understanding. Melting points, boiling points, and viscosity can all be rationalised in terms of the nature and strength of the intermolecular forces that exist between molecules. Therefore, we specify that the sample be kept at constant volume during the heat capacity measurement. In order to make sense of how thermal energy can be formulated from these random fluctuations, we would like to know how many ways does each of these particles can “have energy” and how is the total energy distributed among these different "ways"? Many teachers believe it introduces misconceptions that we spend time unpicking later. When we asked how many ways does each spring in a solid can have energy, the answer was two, one kinetic and one potential. The three states of matter are solid, liquid and gas. The resulting gas particles are free to move in three-dimensions. 2. Compare and group materials together, according to whether they are solids, liquids or gases. To answer this within the constraints of our model, we start with the fact that a spring-mass system has a kinetic and a potential energy. Thus, since rotating the molecule about the x- axis is symmetric, this rotation is not allowed. Agree with the students the criteria that will be used to assess their responses and explain how the assessment will be made. As shown in the figure these are rotations about the y- and z- axes. act as advocate for their partner’s success. Using tools of statistical mechanics (which is beyond the scope of this course) it can be shown that each type of energy that a substance can have, or each mode, has this amount of thermal energy: \[E_{\text{thermal}}(\text {per mode}) = \frac{1}{2}k_{B}T \]. Particles close to one another and randomly organised. You find that when you add the same amount of energy to each container, you measure the same temperature change. They interpret diagrams on cards showing representations of particles and may observe a teacher demonstration. In words the above equation means that temperature is a measure of the average energy in an active mode when the sample is in thermal equilibrium. Thus, the total number of possible modes in a non-linear polyatomic molecule is: 3(KEtrans)+3(KErot)+(3N-6)(KEtrans)+(3N-6)(KEtrans)=6N-6. a) Calculate the heat capacity Cv for the substance in the diagram. One mole of a solid will have \(6N_A\) number of modes, resulting in a total thermal energy of: How many modes do different gases have? But careful! Classify substances as elements, compounds, mixtures, metals, non-metals, solids, liquids, gases and solutions. Share the objectives with the students and explain that they will look at modelling to describe gases, liquids and solids, and to explain differences in their properties. In a diatomic gas, composed of two-atom molecules, such as H2 or O2, there are still no inter-molecular (between molecules) interactions, but there are now intra-molecular (between the atoms within a molecule) interactions to consider. Particle model for solid liquid gas thermodynamics: ahmedelshfie: 9 9954 April 06, 2010, 09:58:33 am by Fu-Kwun Hwang: particle model of liquid in a container (microscopic) misc: ahmedelshfie: 0 5335 June 01, 2010, 06:18:05 pm by ahmedelshfie We can model the bond between the two atoms in a molecule as a spring, allowing the two atoms to vibrate relative to each other. where \(k_{B}=1.38\times10^{-23} J/K\) is the Boltzmann constant and T is temperature. In this model, particles are represented by small solid spheres. From the Energy-Interaction Model when no work is being done and only temperature is changing we have \(\Delta E_{tot}=\Delta E_{th}=Q\). They interpret diagrams on cards showing representations of particles and may observe a teacher demonstration. The energy associate with rotations is known as rotational kinetic energy, KErot. To add up to 3N total kinetic energy modes, \(3N=3+3+(KE_{vib})\), we find that there must be 3N-6 KEvib modes. For a diatomic gas we have found a total of 7 modes: 3 KEtrans, 2 KErot, 1 KEvib, and 1 PEvib. But we need to be careful that we are actually comparing the same things. d) You take two moles of the substance in part a) and one mole of the substance in part b) and place them together in an insulated container. Rotational modes typically have lower energy than vibrational modes. Figure 3.5.3: Possible vibrational modes in a non-linear triatomic molecule. Missed the LibreFest? Students think about gases, liquids and solids in terms of the particle model. We saw here that as thermal energy increases the particles start to vibrate about their equilibrium. Calculate the heat capacity Cv for this substance assuming all modes are active. Heat capacity: \[C_v = nc_{v,mol} = 2\times 7\times \frac{R}{2} = 58.2 J/K\nonumber\]. Legal. Assume there is no change in bond energy in the interval you are analyzing. One way to think about this is that only rotations that change the orientation of the molecule or are not symmetric, are energetically allowed. Ensure that the words gas, liquid and solid are used and understood. Describe and model the structure of the atom in terms of the nucleus, protons, neutrons and electrons; comparing mass and charge of protons neutrond and electrons.

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