Unit 2 review for finals These are the topics you should know and be able to answer questions about: 1. Heating/cooling curve (phase change diagram) a. Draw a heating curve showing a solid melting to a gas temperature b. Draw a cooling curve showing a gas cooling to a solid Gas liquid Solid
c. Look at the phase change diagram below: What state of matter is present between A and B, between C and D, and between E and F? Draw a particle diagram (the circles0 for each phase of matter present. What physical process is occurring from B to C and from D to E? A and B = solid C and D = Liquid E and F = Gas B to C = melting D to E = boiling/evaporating
This picture above has extra info than what you need to know (ie mc and H) but look at the pictures and the phases. This is a good example of what phases are present and when. These pictures can be added to the diagram above. 2. specific heat a. What is the formula for specific heat? - Change of heat = change in temperature x mass x specific heat q = t x m x Cp Joules (J) Celsius ( o C) mass (g) J / g * o C b. How do you solve for the specific heat of a substance? Cp = q / t * m c. How do you solve for the mass of a substance? m = q / t * Cp d. How do you solve for the temperature of a substance? t = q / m * Cp e. 250 J will raise the temperature of 5 g of a metal from 30 o C to 70 o C. What is the specific heat of the metal? Cp = q / t * m Remember to use the change in temperature (70 30 = 40 o C) Cp = 250 J / (40 o C * 5 g) Cp = 1.25 J/g * o C
f. If the specific heat of a substance is 1.5 J/g o C and you add heat to it so that its temperature changes from 25 o C to 60 o C, what is the mass of the metal? m = q / t * Cp Remember to use the change in temperature (60 25 = 35 o C) m = q / (35 o C * 1.5 J/g o C) m = 100 J / (35 o C * 1.5 J/g o C) m = 1.9 g 3. A little review of the phases of matter a. Read the following paragraph and summarize it in your own words. Kinetic Molecular Theory This theory describes all matter as being composed of tiny particles in endless random motion. In a solid, the particles vibrate, but are locked into an orderly array. In a liquid, the particles are still touching but are free to move around past one another. In a gas, the particles are moving very rapidly and are widely separated. When energy is transferred to a sample of matter, either the particles speed up (temperature increases) or they get pulled apart (phase change), but not both at the same time. This helps account for the shape of the warming curve you got in the Icy Hot lab. You should have a summary of the reading Phase is changing b. Temperature is increasing c. Look at the above heating curve, where is the temperature increasing? Where is the phase changing? - Temperature increases when the heating curve is diagonal - The phase changes when the heating curve is flat
d. If the amount of water used in the heating curve above was doubled, what would happen to the phase change diagram would the melting and boiling point increase? Would the melting and boiling point decrease? Or would the melting and boiling point remain the same, but the time it took to reach these two points would increase? Why? - The melting and boiling point would not change. This is because the mp and bp are unique for every substance. It does not matter how much of the substance you have, the mp and bp are always the same. - What would increase would be the time it takes to reach the melting and boiling point. The more substance you have, the longer it takes to heat up a substance to its melting and boiling point. visually it would look like this - same mp and bp, just takes longer to reach these points e. The graph at right represents the temperature time behavior of what was initially a sample of ice at 0 C. Use the following choices for the next few questions A. increasing B. decreasing C. the same D. zero a. During region B the temperature (kinetic energy) is increasing. b. During region C the temperature (kinetic energy) is remaining the same. c. During region A the potential energy is increasing due to the phase change.. Remember that temperature and kinetic energy are related. As the temperature increases, the kinetic energy increases. This means that as the temperature increases, the molecules move around faster. Also, that phase change and potential energy are related. As the phases change, the potential energy increases. This is because the molecules gain potential energy as they are moving away from each other. Since the molecules are moving away from each other during a phase change, then the potential energy is increasing during a phase change.
4. Review of the classification of matter: a. Which of the following pictures is a solid? Gas liquid solid gas Covalent compound element/atoms ionic compound element and Pure substance pure substance pure substance covalent compound Mixture
Matter Gas Liquid Solid Pure substance Mixture Element Compound Homogeneous Heterogeneous Heterogeneous Matter Pure Substance Elements Homogeneous Liquid Solid Mixtures Compounds Gases
5. What is in between gas particles in a closed container? Empty space = nothing 6. What is in the bubbles of boiling water? Water vapor boiling water is a physical change, so you still have water, just a different phase of it 7. The gas in the box at left has a higher temperature than the gas in the box at the right. Draw whooshies or arrows on the particles in each box to represent their relative motion. Explain. The left box will have longer whooshies or arrows because the particles are moving faster since they are at a higher temperature a. If the number of particles in the left box above were doubled, what would happen to the pressure of the gas? Explain. - The pressure would increase because the more particles there are, the more often they are colliding with the walls of the container and with each other. Every time the particles collide, they are increasing the pressure. 8. pressure vs. number of particles a. What happens to the pressure of a gas as the number of particles increases? - The pressure increases because the particles are colliding more often 9. temperature vs. volume a. What happens to the volume of a gas as the temperature of the gas increases? - The volume increases, because the particles are moving faster and expanding 10. volume vs. pressure a. When the volume of a container of gas is decreased, what happens to the pressure of the gas? - Pressure increases because the particles have less room to move around so they collide more often b. When the volume of a container of gas is increased, what happens to the pressure of the gas? - Pressure decreases because the particles have more room to move around so they collide less often 11. Gas Laws a. What is the formula for Charles law? T2V1 = T1V2 b. What is the formula for Boyle s law? P1V1 = P2V2 c. What is the formula for the combined gas law? P1V1T2 = P2V2T1
d. How do you convert from degrees Celsius to Kelvin? - Add 273 to your degrees Celsius e. How do you convert from ml to l? - You divide by 1000 ml Number of ml 1 L ------------------ x ----------- = L 1 1000 ml f. How hot will a 2.3 L balloon have to get to expand to a volume of 400 L? Assume that the initial temperature of the balloon is 25 0 C. - Since we have temperature and volume, this is Charles Law - We cannot be in Celsius though, so we need to add 273 to the 25 o C to get 298 K T2V1 = T1V2 T2(2.3 L) = (298 K)(400 L) T2 = 51826 K g. If the tire pressure is initially 30 psi at 25.0 C, what is the temperature of the air inside the tire when the pressure increases to 100.0 psi? Assume tire volume is constant. - Since we have pressure, temperature and a constant temperature, this is the combined gas law - Remember that we cannot be in Celsius, so we add 273 to 25 o C to get 298 K - Remember that if you are told that a variable is constant that you use the number 1 to represent it in the formula P1V1T2 = P2V2T1 (30 psi)(1)t2 = (100 psi)(1)(298 K) T2 = 993 K 12. Putting all of the gas laws together: a. The diagram below left shows a representation of a sample of gas at 50 C. Which of the following best represents the same gas at 0 C? You would solve this first by completing a gas law problem Since we have temperature and volume, this is Charles law (assume the volume of the box is 100 as in 100% full to begin with) Since we are in Celsius, we have to add 273 to get to Kelvin 50 o C = 50 + 273 = 323 K 0 o c + 273 = 273 K T2V1 = T1V2 (273 K)(100%) = (323)V2 V2 = 84% This would be box letter B approx