Northwestern Agusan Colleges
Bayview Hill, Nasipit, Agusan del Norte
GENERAL Chemistry 2
1st Quarter
Senior High School
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An in-depth exploration of the properties of solids and liquids, focusing on intermolecular forces, surface tension, viscosity, vapor pressure, boiling point, molar heat of vaporization, and the kinetic molecular theory. It also delves into the properties of solutions, solubility, stoichiometry of reactions in solutions, energy changes in chemical reactions, and the role of activation energy and catalysts in reaction rates.
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2019/2020
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Northwestern Agusan Colleges
Bayview Hill, Nasipit, Agusan del Norte
GENERAL Chemistry 2
st
Quarter
Senior High School
__________________________________________________
NAME:
________________________
Grade & Strand:
This lesson explores the kinetic molecular theory and how it pertains to the properties of solids and liquids. You'll learn the properties of solids and liquids, discover the types of intermolecular attractions that occur between them and gain an understanding how phase changes happen. Kinetic Molecular Theory Take a glass of water. Drop a few drops of red food coloring in it. What happens? The red food coloring drops should make their way down the glass of water slowly, spread out and finally tint all of the water a reddish color. Why does this happen? It happens because both substances are made out of molecules that are constantly moving. These molecules have energy; one of the fundamental principles of the kinetic molecular theory. The Kinetic Molecular Theory (KMT) is a model used to explain the behavior of matter. It is based on a series of postulates. Some of the postulates of KMT are as follows:
- Matter is made of particles that are constantly in motion. This energy in motion is called kinetic energy.
- The amount of kinetic energy in a substance is related to its temperature.
- There is space between particles. The amount of space in between particles is related to the substance's state of matter.
- Phase changes happen when the temperature of the substance changes sufficiently.
- There are attractive forces in between particles called intermolecular forces. The strength of these forces increase as particles get closer together. In this lesson, we will focus on how KMT can be used to explain the properties of liquids and solids. KMT and Properties of Liquid One is a photo of water in a swimming pool; the other is of liquid water on the molecular level. What properties of liquids are evident in these two pictures? One of the most notable properties of liquids is that they are fluid and they can flow. Liquids have definite volume, but not a definite shape. Liquids are said to have low compressibility; LESSON 1 : Kinetic Molecular and Intermolecular Forces
Week 1 - 2
At the end of the lesson, I can: ➢ Use the kinetic molecular model to explain properties of liquids and solids (MELCS) ➢ Describe and differentiate the types of intermolecular forces ➢ Describe the following properties of liquids, and explain the effect of intermolecular forces on these properties: surface tension, viscosity, vapor pressure, boiling point, and molar heat of vaporization Figure 1.1. Water in pool and at molecular level
Types of Intermolecular Forces Intermolecular forces are electrostatic in nature and include van der Waals forces and hydrogen bonds. Molecules in liquids are held to other molecules by intermolecular interactions, which are weaker than the intramolecular interactions that hold the atoms together within molecules and polyatomic ions. Transitions between the solid and liquid or the liquid and gas phases are due to changes in intermolecular interactions but do not affect intramolecular interactions. The three major types of intermolecular interactions are dipole–dipole interactions, London dispersion forces (these two are often referred to collectively as van der Waals forces), and hydrogen bonds. Dipole–dipole interactions arise from the electrostatic interactions of the positive and negative ends of molecules with permanent dipole moments; their strength is proportional to the magnitude of the dipole moment and to 1/ r^3 , where r is the distance between dipoles. London dispersion forces are due to the formation of instantaneous dipole moments in polar or nonpolar molecules as a result of short-lived fluctuations of electron charge distribution, which in turn cause the temporary formation of an induced dipole in adjacent molecules. their energy falls off as 1/ r^6. Larger atoms tend to be more polarizable than smaller ones because their outer electrons are less tightly bound and are therefore more easily perturbed. Hydrogen bonds are especially strong dipole–dipole interactions between molecules that have hydrogen bonded to a highly electronegative atom, such as O, N, or F. The resulting partially positively charged H atom on one molecule (the hydrogen bond donor ) can interact strongly with a lone pair of electrons of a partially negatively charged O, N, or F atom on adjacent molecules (the hydrogen bond acceptor ). Because of strong O⋅⋅⋅H hydrogen bonding between water molecules, water has an unusually high boiling point, and ice has an open, cage like structure that is less dense than liquid water. Figure 1. 3. Types of Intermolecular Forces
Intermolecular forces and their effect on properties of liquids
Intermolecular (or interparticle ) forces are weak interactions between particles. They
decrease as you go from solid → liquid → gas. Remember that in a gas the particles have
the highest degree of freedom of movement and negligible or weak intermolecular forces.
As the intermolecular attraction increases,
- The vapor pressure ( the pressure of the vapor that is in equilibrium with its liquid) decreases
- The boiling point ( the temperature at which the vapor pressure becomes equal to the pressure exerted on the surface of the liquid) increases
- Surface tension ( the resistance of a liquid to spread out and increase its surface area) increases
- Viscosity ( the resistance of a liquid to flow) increases. Higher the intermolecular forces between the liquid particles, harder it is for it to escape into the vapor phase, ie., you need more energy to convert it from liquid to the vapor phase, in other words, higher its boiling point. Fluid =A gas or a liquid; a substance that can flow. Surface tension =The measure of the elastic force in the surface of a liquid. It is the amount of energy required to stretch or increase the surface of a liquid by a unit area. Capillary action= The tendency of a liquid to rise in narrow tubes or to be drawn into small openings Viscosity =A measure of a fluid’s resistance to flow. Vapor = A gaseous substance that exist naturally as a liquid or solid at normal temperature Vaporization = The change of phase from liquid to vapor (gaseous phase). Vapor pressure of a liquid =The equilibrium pressure of a vapor above its liquid; that is, the pressure exerted by the vapor above the surface of the liquid in a closed container. Boiling point= The temperature at which a liquid boil. The boiling point of a liquid when the external pressure is 1 atm is called the normal boiling point. Molar heat of vaporization (ΔHvap) = The energy (usually in kilojoules) required to vaporize 1 mole of a liquid at a given temperature
VOCABULARY
What is Concentration of Solution? The Concentration of a Solution is defined as the relative amount of solute present in a solution. It basically talks about how to find the amount of solute present in solvent which together forms solution. There are various methods used to find this, Methods of Expressing Concentration of Solutions
- Percentage by weight (w / w %)
- Percentage by volume (V / V%)
- Weight by volume (w / v%)
- Mole fraction (x)
- Parts per million (ppm)
- Molarity (M)
- Molality (m) Percentage by Weight Symbol: (w / w %) Definition: It is defined as the amount of solute present in 100 g of solution. Percentage by Volume Symbol: (V / V %) Definition: It is defined as the volume of solute present in 100 mL of solution. Weight by Volume Symbol: (W / V %) Definition: It is defined as the amount of solute present in 100 mL of solution. Unit: mg/L LESSON 2 : Properties of solutions, solubility, and the stoichiometry of reactions in solutions
Week 3 - 4
At the end of the lesson, I can: ➢ Use different ways of expressing concentration of solutions: percent by mass, mole fraction, molarity, molality, percent by volume, percent by mass, ppm (MELCS) ➢ Perform stoichiometric calculations for reactions in solution ➢ Describe the effect of concentration on the colligative properties of solutions
Mole Fraction Symbol : X ( lower-case Greek letter chi, χ) Definition: It is the ratio of the number of moles of solute and the total number of moles of solute and solvent. Parts Per Million Symbol: ppm Definition: It is defined as the parts of a component per million parts (1 06 ) of the solution. It is widely used when a solute is present in trace quantities. Unit: ppm Molarity: Symbol : M Definition: Molarity of any solution is number of moles of solute per liter of solution Unit: mol/litre Formula: Molarity = Number of moles of solute / Volume of solution in liter. Molality Symbol: m Definition: Molality of any solution is represented as the number of moles of solute present per kg of solvent Unit: mol/kg Formula: Molality(m) = Number of moles of solute / Mass of solvent in Kg Note: Why m is not affected by change in temperature? Since it is dependent on mass of solute and mass do not change to small shift in temperature due to close packing of solid atoms therefore it is independent of temperature change. Solve the problem below:
- As an example consider 5 g sugar dissolved in 20 g of water. What is the w/w% concentration of sugar in this solution?
- What are the mole fraction of the components of the solution formed when 92 g glycerol is mixed with 90 g water? (molecular of weight water = 18; molecular weight of glycerol = 92).
- What is the molarity of a solution containing 0.32 moles of NaCl in 3.4 liters? Let’s Test
All changes that matter undergoes, whether physical or chemical, occur with loss or gain of energy. Burning of fuel gas releases energy in the form of heat and light as the fuel reacts with oxygen in air. This means that the energy content of the combustion products, carbon dioxide, and water is lower compared to that of C 4 H 10 and oxygen gas. The difference in energy is released as heat and light. Heat, also referred to as thermal energy, is the energy transferred between two bodies due to a difference in their temperatures. Similarly, in a physical transformation such as dew formation, energy is released during the process since the heat content of the liquid form (dew) is lower than that of the vapor from which the dew is formed. These changes that produce or release energy are said to be exothermic. In contrast, chemical and physical changes that occur with the absorption of energy are referred to as endothermic process. The First Law of Thermodynamics Also known as the law of conservation of energy, states that “ energy cannot be created or destroyed but can simply be converted to another forms of energy.” Mathematically, this is represented as ΔU=q+w with
- ΔU is the total change in internal energy of a system,
- q is the heat exchanged between a system and its surroundings, and
- w is the work done by or on the system. LESSON 3: Energy changes in chemical reactions
Week 5 - 6
At the end of the lesson, I can: ➢ Explain the first law of thermodynamics (MELCS) ➢ Explain enthalpy of a reaction ➢ Calculate the change in enthalpy of a given reaction using Hess Law Determine which of the following process are endothermic or exothermic.
- Cutting of paper
- Rotation of the blades of an electric fan
- Digestion of food.
- Decomposition of waste in a compost heap Try This
Energy in different forms: Potential energy is stored energy. Matter possesses potential chemical energy. Kinetic energy is energy in motion. Gas particles which are always in motion possess high kinetic energy. Molecules in a liquid, whose motion are more restricted compared to gas molecules, possess lower kinetic energy. Mechanical energy is energy at work. A man who pedals a running bicycle does mechanical energy. Thermal energy is heat energy. The warmth that you feel on a summer day manifests heat energy caused by the difference in temperature between your body and your environment. Electrical energy is the energy of the mobile electrons that produce electricity. Heats of formation Enthalpy is the total heat absorbed in a process at constant pressure if the only work done is pressure-volume work. It is the sum of the internal energy of the system and the product of pressure and volume. Enthalpy can be described by the equation: Calculating Enthalpy of Reaction from Standard Enthalpies of Formation Because enthalpy of reaction is a state function the energy change between reactants and products is independent of the path. We can choose a hypothetical two step path where the atoms in the reactants are broken into the standard state of their element), and then from this hypothetical state recombine to form the products Note the first step is the opposite of the process for the standard state enthalpy of formation, and so we can use the negative of those chemical species's ΔHformation. Solve the problem below:
A gas in a system has constant pressure. The surroundings around the system lose 62 J
of heat and does 474 J of work onto the system. What is the internal energy of the
system?
Let’s Test H= U + PV
Reaction Rate During the course of the reaction shown on figure 4.1, reactants A and B are consumed while the concentration of product AB increases. The reaction rate can be determined by measuring how fast the concentration of A or B decreases, or by how fast the concentration of AB increases. A+B⟶AB For the stoichiometrically complicated Reaction: Looking at Figure 4.1 above, we can see that the rate can be measured in terms of either reactant (A or B) or either product (C or D). Not all variables are needed to solve for the rate. Therefore, if you have the value for "A" as well as the value for "a" you can solve for the reaction rate. You can also notice from Equation above that the change in reactants over the change in time must have a negative sign in front of them. The reason for this is because the reactants are decreasing as a function of time, the rate would come out to be negative (because it is the reverse rate). Therefore, putting a negative sign in front of the variable will allow for the solution to be a positive rate. Chemical reactions vary greatly in the speed at which they occur. Some are ultrafast, while others may take millions of years to reach equilibrium. LESSON 4 : the rate of a reaction and the various factors that influence it
Week 7 - 8
At the end of the lesson, I can: ➢ Describe how various factors influence the rate of a reaction (MELCS) ➢ Differentiate zero, first-, and second-order reactions ➢ Explain reactions qualitatively in terms of molecular collisions ➢ Explain activation energy and how a catalyst affects the reaction rate ➢ Cite and differentiate the types of catalysts Figure 4.1: The above picture shows a hypothetical reaction profile in which the reactants (red) decrease in concentration as the products increase in concentration (blue).
Definition of Reaction Rate The Reaction Rate for a given chemical reaction is the measure of the change in concentration of the reactants or the change in concentration of the products per unit time. The speed of a chemical reaction may be defined as the change in concentration of a substance divided by the time interval during which this change is observed: For a reaction of the form A+B→CA+B→C, the rate can be expressed in terms of the change in concentration of any of its components in which Δ[A] is the difference between the concentration of A over the time interval t 2 – t 1 : Δ[A]=[A] 2 – [A] 1 Notice the minus signs in the first two examples above. The concentration of a reactant always decreases with time, so Δ[A] and Δ[A] are both negative. Since negative rates do not make much sense, rates expressed in terms of a reactant concentration are always preceded by a minus sign to make the rate come out positive. Reaction Order The reaction rate for a given reaction is a crucial tool that enables us to calculate the specific order of a reaction. The order of a reaction is important in that it enables us to classify specific chemical reactions easily and efficiently. Knowledge of the reaction order quickly allows us to understand numerous factors within the reaction including the rate law, units of the rate constant, half-life, and much more. Reaction order can be calculated from the rate law by adding the exponential values of the reactants in the rate law. Rate=k[A]s[B]t Reaction Order=s+t It is important to note that although the reaction order can be determined from the rate law, there is in general, no relationship between the reaction order and the stoichiometric coefficients in the chemical equation.AIs shown in the equation above, the complete reaction order is equal to the sum of "s" and "t." But what does each of these variables mean? Each variable represents the order of the reaction with respect to the reactant it is placed on. In this certain situation, s is the order of the reaction with respect to [A] and t is the order of the reaction with respect to [B]. Try This
Collision Theory Chemical reactions have been a part of this world ever since everything began. From Big bang to the present day, everything happening around us has something to do with chemical reactions and chemical processes. Chemical reactions are common in our daily lives: from cooking, eating, cleaning to the different chemical processes like respiration, corrosion and fermentation. How our body lives and grows are results of many chemical reactions that takes place, although you may not recognize them. This is the reason we need to understand how chemical processes takes place, be it naturally occurring or not. All substances are comprised of millions of tiny particles in constant motion. These particles are colliding with each other constantly in any substance. All collisions between particles do not result in a reaction. There are two factors that determine whether a reaction will occur between two particles that are colliding:
- Substances or particles of reactants must physically collide with enough energy
- Substance or particles must come into contact or collide in the correct orientation (facing the correct way). The collision theory states that reacting substances must come into contact (collide) with enough activation energy, and in the correct orientation (facing the correct way), so that their electron shells can rearrange to form the products of the reaction. Therefore, any factor which changes the frequency or energy of the collisions will change the rate of the reaction. Factors Affecting the Rate of Reaction Activation Energy refers to the minimum energy required for a reaction to take place. When a collision provides energy equal to or greater than the activation energy, product can form. On the other hand, if the particles have energy that is less than the activation energy, the collision is not effective, and they just bounce off each other unchanged. The figure above shows a man trying to push a rock over the cliff. For the man to push the rock, he needs to have enough energy. If the man does not have enough energy, the rock will not move down the cliff. This energy needed for the man to push the rock over the cliff represents the activation energy. Chemical or Physical Change? Directions: Identify what kind of change occurs by writing the word Physical change or Chemical change. Try This
Temperature refers to how hot or cold a certain substance is. Usually, a rise in temperature of 10 0C doubles the reaction rate. The rate of a chemical reaction increases with increasing temperature. As the temperature increases, collision between atoms and molecules becomes faster resulting to build up of more energy. The increased kinetic energy will equal to or exceed the activation energy resulting to more collisions giving rise to a reaction. Concentration , the rate of a chemical reaction is affected by the concentration of reacting substances. The term concentration refers to the number of particles present in a given volume of solution. Concentration may also mean a measure of how much of of the solute (something to be dissolved) is dissolved in a solvent (dissolving medium) to form a homogeneous mixture. So, a higher concentration means there is more of the solute in the solution. If the concentration of the reactant is increased, the rate of reaction also increases. When the number of particles of the reactant is increased, there is a great chance for particles to collide. Surface area is the measure of how much exposed area a solid object has, expressed in square units. In a reaction between a solid and a liquid, the more finely divided a solid is, the faster is the rate of reaction. Likewise, as you powdered a solid, its surface area becomes greater, thus the particles have higher chance of colliding and faster reaction happens. Catalyst Reaction rates generally increase with increasing reactant concentration, increasing temperature, and the addition of a catalyst. Physical properties such as high solubility also increase reaction rates. Solvent polarity can either increase or decrease the rate of reaction, but increasing solvent viscosity generally decreases reaction rates. Arrange the following samples according to the rate of solubility of sugar. (1 - fastest, 3-slowest). Try This Fill in the blanks to complete the passage. Increasing the ___________ of a system increases the average kinetic energy of its constituent particles. As the average kinetic energy increases, the particles move faster and collide more frequently per unit time and possess greater energy when they collide. When the ___________ of all the reactants increases, more molecules or ions interact to form new compounds, and the rate of reaction increases. When solids and liquids react, increasing the surface area of the solid will increase the reaction rate. A decrease in ___________ causes an increase in the solid’s total surface area. Collisions only result in a reaction if the particles collide with a certain minimum energy called the ___________ for the reaction. The position of activation energy can be determined on a Maxwell-Boltzmann distribution. To increase the rate of a reaction, the number of successful collisions must be increased. One possible way of doing this is to provide an alternative way for the reaction to happen which has a lower activation energy. Adding ___________ has this effect on activation energy. It provides an alternative route for the reaction with a lower activation energy. Catalysts are everywhere! Many biochemical processes, such as the oxidation of glucose, are heavily dependent on ___________, proteins that behave as catalysts Let’s Test