Heat and Energy J Deutsch

2 Energy can exist in different forms, such as chemical, electrical, electromagnetic, thermal, mechanical, and nuclear. Kinetic energy – the energy of motion Potential energy – the energy of position (stored energy)

J Deutsch Heat is a transfer of energy (usually thermal energy) from a body of higher temperature to a body of lower temperature. Thermal energy is the energy associated with the random motion of atoms and molecules. The Law of the Conservation of Energy states that energy can neither be created nor destroyed.

J Deutsch Temperature is a measurement of the average kinetic energy of the particles in a sample of material. Temperature is not a form of energy. Two temperature scales used in chemistry are Celsius and Absolute The unit of temperature in the Celsius scale is the degree (ºC) The unit of temperature on the Absolute scale is the Kelvin (K)

J Deutsch To convert between absolute and Celsius temperature scales use K=ºC+273

J Deutsch Regents Question: 06/03 #41 The freezing point of bromine is (1) 539°C (2) –539°C (3) 7°C (4) –7°C See Table S Melting point is the same as freezing point Convert K to C (K=C+273)

J Deutsch The concepts of kinetic and potential energy can be used to explain physical processes that include: fusion (melting), solidification (freezing), vaporization (boiling, evaporation), condensation, sublimation, and deposition. Add energy (endothermic) subliming meltingboiling SOLIDLIQUIDGAS Remove energy (exothermic) freezing depositing condensing

J Deutsch Regents Question: 06/03 #17 Which change is exothermic? (1) freezing of water (2) melting of iron (3) vaporization of ethanol (4) sublimation of iodine

J Deutsch A change in phase is a change in Potential Energy, not Kinetic Energy Potential energy changes so temperature doesn’t Boiling Point Melting Point

J Deutsch Energy and phase changes  AB - solid warms up (KE inc/PE constant)  BC- solid melts (KE constant/PE inc)  CD – liquid warms up (KE inc/PE constant)  DE- liquid boils (KE constant/PE inc)  EF – gas warms (KE inc/PE constant)

J Deutsch Regents Question: 06/02 #16 Which change in the temperature of a 1-gram sample of water would cause the greatest increase in the average kinetic energy of its molecules? (1) 1°C to 10°C (3) 50°C to 60°C (2) 10°C to 1°C(4) 60°C to 50°C

J Deutsch Heat is transferred to different materials at different rates.  The specific heat capacity (C) determines the rate at which heat will be absorbed.  The specific heat capacity for water is 4.18J/g  The quantity of heat absorbed (Q) can be calculated by: Q=mC  T m=mass  T=change in temperature

J Deutsch Regents Question: 06/02 #28 As ice melts at standard pressure, its temperature remains at 0°C until it has completely melted. Its potential energy (1) decreases (2) increases (3) remains the same

J Deutsch Regents Question: 08/02 #54 A sample of water is heated from a liquid at 40°C to a gas at 110°C. The graph of the heating curve is shown in your answer booklet. a On the heating curve diagram provided in your answer booklet, label each of the following regions: Liquid, onlyGas, onlyPhase change Liquid Only Gas Only Phase change

J Deutsch Regents Question: cont’d b For section QR of the graph, state what is happening to the water molecules as heat is added. c For section RS of the graph, state what is happening to the water molecules as heat is added. They move faster, their temperature increases. Their intermolecular bonds are breaking, their potential energy is increasing.

J Deutsch Regents Question: 01/02 #47 What is the melting point of this substance? (1) 30°C(3) 90°C (2) 55°C (4) 120°C

J Deutsch The quantity of energy absorbed or released during a phase change can be calculated using the Heat of Fusion or Heat of Vaporization  Melting (fusion) or freezing (solidification) –Q=mH f where H f is the heat of fusion (for water: J/g)  Boiling (vaporization) or condensing –Q=mH v where H v is the heat of vaporization (for water: 2259 J/g) H f and Hv are given to Table B – m is the mass

J Deutsch Regents Question: 08/02 #24 In which equation does the term “heat” represent heat of fusion? (1) NaCl(s) + heat  NaCl(l) (2) NaOH(aq) + HCl(aq)  NaCl(aq) + H 2 O(l)+ heat (3) H 2 O(l)+ heat  H 2 O(g) (4) H 2 O(l)+ HCl(g)  H 3 O + (aq) + Cl – (aq) + heat Fusion refers to melting.

J Deutsch Melting Point  The temperature at which a liquid and a solid are in equilibrium  The melting point for ice is 0ºC  The melting point of a substance is the same as its freezing point

J Deutsch Regents Question: 08/02 #5 Given the equation: H 2 O(s) H 2 O(l) At which temperature will equilibrium exist when the atmospheric pressure is 1 atm? (1) 0 K (3) 273 K (2) 100 K(4) 373 K K=C + 273

J Deutsch Regents Question: 08/02 #18 The solid and liquid phases of water can exist in a state of equilibrium at 1 atmosphere of pressure and a temperature of (1) 0°C (3) 273°C (2) 100°C(4) 373°C

J Deutsch Regents Question: 06/02 #13 The strongest forces of attraction occur between molecules of (1) HCl (3) HBr (2) HF (4) HI

J Deutsch These properties include conductivity, malleability, solubility, hardness, melting point, and boiling point.  The stronger the intermolecular forces, the higher the boiling point and melting point.  The stronger the intermolecular forces, the lower the vapor pressure. –See Table H

J Deutsch A liquid will boil when its vapor pressure equals the atmospheric pressure.  Raising the temperature will increase the vapor pressure of the liquid  Lowering the atmospheric pressure will lower the boiling point –On top of a high mountain, water boils at a temperature below 100  C

J Deutsch Table H – the vapor pressure of four liquids at various temperatures. As temp inc, vapor pressure inc.

J Deutsch Regents Question: 06/03 #40 According to Reference Table H, what is the vapor pressure of propanone at 45°C? (1)22 kPa (2)33 kPa (3)70. kPa (4) 98 kPa

J Deutsch Standard pressure is kilopascals (kPa) or 1 atmoshpere (atm) The normal boiling point occurs when the atmospheric pressure is kPa (standard pressure) The normal boiling point of ethanol is 80ºC.

J Deutsch Regents Question: 08/02 #28 As the pressure on the surface of a liquid decreases, the temperature at which the liquid will boil (1) decreases (2) increases (3) remains the same

J Deutsch Regents Question: 08/02 #30 As the temperature of a liquid increases, its vapor pressure (1) decreases (2) increases (3) remains the same

J Deutsch Regents Question: 08/02 #44 The vapor pressure of a liquid is 0.92 atm at 60°C. The normal boiling point of the liquid could be (1) 35°C (3) 55°C (2) 45°C (4) 65°C The normal boiling point is the temperature at which a liquid boils when the atmospheric pressure is standard pressure (1 atm or kPa)

J Deutsch Regents Question: 01/03 #68 What is the vapor pressure of liquid A at 70°C? Your answer must include correct units. 700 mm Hg

J Deutsch Regents Question: 01/03 #69 At what temperature does liquid B have the same vapor pressure as liquid A at 70°C? Your answer must include correct units. 113°C

J Deutsch Regents Question: 01/03 #70 Which liquid will evaporate more rapidly? Explain your answer in terms of intermolecular forces. Liquid A will evaporate more rapidly because, at any temperature, it has the higher vapor pressure.

J Deutsch The amount of thermal energy contained in the molecules depends on how fast they are moving and how many molecules there are.  The total kinetic energy of all the molecules combined is called thermal energy  Thermal energy is a result of the Kinetic Energy of the molecules’ motion (molecules are always moving.)  Which can melt more ice: a small cup of hot water or a swimming pool of cold water?

J Deutsch The concept of an ideal gas is a model to explain the behavior of gases. A real gas is most like an ideal gas when the real gas is at low pressure and high temperature.

J Deutsch Kinetic molecular theory (KMT) for an ideal gas states that all gas particles :  1. are in random, constant, straight-line motion.  2. are separated by great distances relative to their size; the volume of the gas particles is considered negligible.  3. have no attractive forces between them.  4. have collisions that may result in the transfer of energy between gas particles, but the total energy of the system remains constant.

J Deutsch Real Gases  Molecules do take up space  Molecules do attract each other  Energy is lost during collisions  Under conditions of high temperature and low pressure, real gases behave more like ideal gases  Hydrogen and helium are closest to being ideal gases

J Deutsch Collision theory states that a reaction is most likely to occur if reactant particles collide with the proper energy and orientation. Anything that will increase the number of effective collisions will increase the rate at which the reaction will occur:

J Deutsch Kinetic molecular theory describes the relationships of pressure, volume, temperature, velocity, and frequency and force of collisions among gas molecules. P1V1P2V2P1V1P2V2 T 2

J Deutsch Gas Laws  Boyle’s Law –Indirect Relationship between pressure and volume –Temperature remains constant –PxV = constant  Charles’ law –Direct relationship between volume and temperature –Pressure remains constant –V/T = constant –Temperature must be Absolute temperature (Kelvins)

J Deutsch Graphing the gas laws Volume Temperature Pressure Volume Temperature Pressure As absolute temperature increases, pressure increases at constant volume As absolute temperature increases, volume increases at constant pressure As pressure increases, volume decreases at constant temperature

J Deutsch Regents Question: 06/02 #14 Which graph shows the pressure-temperature relationship expected for an ideal gas?

J Deutsch Regents Question: 06/02 #15 At the same temperature and pressure, which sample contains the same number of moles of particles as 1 liter of O 2 (g)? (1) 1 L Ne(g)(3) 0.5 L SO 2 (g) (2) 2 L N 2 (g) (4) 1 L H 2 O(l)

J Deutsch Equal volumes of different gases at the same temperature and pressure contain an equal number of particles. Avogadro’s Hypothesis