solid IMF>liquid IMF>gas IMF Draw a diagram to represent the 3 common states of matter of a given substance: solid liquid gas

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1 Thermochemistry Part 1 Notes States of Matter and Intermolecular Forces (IMF) Chemistry HP At the end of this unit, students should be able to: Describe the various states of matter in terms of kinetic energy, arrangement of particles, intermolecular forces, and properties. Define and describe the 6 common phase changes. Calculate the heat change of a substance during a phase change or temperature change Identify, compare and contract phase changes as endothermic or exothermic. Describe the phase changes of a substance using a heating/cooling curve. Read, interpret, and label a heating curve and a phase diagram What is an intermolecular force (IMF)? What are the relative IMFs in the 3 common states of matter? IMF represent the attractive forces between particles of a particular substance. The general trend for IMFs for a particular substance is solid IMF>liquid IMF>gas IMF Draw a diagram to represent the 3 common states of matter of a given substance: solid liquid gas What is a phase change? Phase change represent the transformation of a thermodynamic system from one state of matter to another by way of heat transfer. In order to change from one phase to another, energy must either be absorbed or released. Often this absorption or release of energy occurs in the form of heat transfer.

2 What are the six common phase changes? Phase Transition Fusion (Melting) (solid to liquid) Vaporization (liquid to gas) Sublimation (solid to gas) Freezing (liquid to solid) Condensation (gas to liquid) Deposition (gas to solid) Direction of ΔH System, surroundings, and universe The system is the chemical reaction under study. The surroundings is every place in the universe except the system. The universe is the system and the surroundings. All chemical reactions either release or require (absorb) energy when they occur. Another way of saying this is that reactions either give off or take in energy. Exothermic reactions:an exothermic reaction is a reaction in which heat is released by the system to the surroundings. From the perspective of the system, heat is given off. For an exothermic reaction, the sign of ΔH is negative Endothermic reactions An endothermic reaction is a reaction in which heat is absorbed by the system from the surroundings. From the perspective of the system, heat is taken in. For an endothermic reaction, the sign of ΔH is positive Enthalpy: Heat energy is referred to in this course as enthalpy (H). Most chemical reactions occur at constant P, so Heat transferred at constant P = qp qp = H where H = enthalpy Enthalpy is the heat absorbed or released by a system at constant pressure. It is impossible to measure enthalpy directly. Only changes in enthalpy are used in this course. We only use ΔH and ΔH = H final - H initial Units of heat energy. We will use joules (J), kilojoules (kj) and calories 1 cal= J How is heat different from temperature? Heat Heat is the transfer of energy between two objects due to temperature differences. heat energy of an object is the SUM of all the kinetic energies of the molecules of the object Heat is dependent on mass, temperature change and specific heat (Extensive property) Temperature Temperature is a measure of how hot or cold a substance is Temperature on the other hand is the AVERAGE of the kinetic energies of all the molecules of the object. Temperature is intensive i.e does not depend of the amount of the substance Heat is measured in Joules, kj or calories Temperature is measured in Kelvin (K) or Celsius (C)

3 The Nature of Water: Water has the chemical formula H 2O and has a bent molecular structure resulting in the molecule being polar. Due to this polarity, the water molecules are attracted to one another and form a type of bond called hydrogen bonds between molecules. Hydrogen bonds represent an IMF and can be represented as shown below. The degree of hydrogen bonding in water depends on the phase of the water molecules. In solid water, ice, virtually 100 % of water molecules are involved in hydrogen bonding. In liquid water, approximately 90% of water molecules are involved in hydrogen bonding. In gaseous water, steam, there is no significant amount of hydrogen bonding. Heating and Cooling Curve Diagrams What is the heating curve? The heating curve is a graph which represents how a sample changes. As heat is added over time, the sample changes temperature and phase accordingly. Interpreting the Graph The slanted portions temp is changing Single phase is heating up or cooling down KE is changing The flat portions temp not changing Substance undergoing a phase change PE is changing Why is the curve flat at some portions? Temperature is staying constant, but potential energy is increasing During this time the solid completely becomes liquid This is called the heat of fusion (H f) in segment BC and heat of vaporization (H v) in segment DE. Remember fusion is melting and vaporization is evaporation All Phase changes accompanied by energy changes Phase changes are physical changes:

4 Heating Curve for Water Label the phases present (s, l, g) and the phase changes (s l and l g) on the heating curve for water. Label and state the melting point and boiling point for water. In the first slanted region of the curve, the temperature of the ice is and the molecules are moving. Once the temperature reaches C, the ice begins to. When the ice melts, heat energy is used to some of the hydrogen bonds between molecules. On the curve, the region where the ice is melting is because the temperature increase. Once enough hydrogen bonds have been broken, the water is liquid. In the second slanted region of the curve, the temperature of the liquid water is and the molecules are moving. Once the temperature reaches C, the water begins to. When the water boils, heat energy is used to hydrogen bonds between molecules. On the curve, the region where the water is boiling is because the temperature increase. Once all the hydrogen bonds have been broken, the water is a gas. In the third slanted region of the curve, the temperature of the steam is and the molecules are moving.

5 Cooling Curve for Water Label the phases present (s, l, g) and the phase changes (g l and l s) on the cooling curve for water Label and state the freezing point and condensing point for water. In the first slanted region of the curve, the temperature of the steam is and the molecules are moving. Once the temperature reaches C, the steam begins to. When the steam condenses, heat energy is released to some hydrogen bonds between molecules. On the curve, the region where the steam is condensing is because the temperature decrease. Once enough hydrogen bonds have been broken, the steam is liquid. In the second slanted region of the curve, the temperature of the liquid water is and the molecules are moving. Once the temperature reaches C, the water begins to. When the water freezes, heat energy is used to hydrogen bonds between molecules. On the curve, the region where the water is freezing is because the temperature increase. Once all the hydrogen bonds have been formed, the water is solid ice. In the third slanted region of the curve, the temperature of the ice is and the molecules are moving.