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Semester 2 Review May 30 and 31, 2013. Acids and Bases 3 Standards 18 Questions.

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Presentation on theme: "Semester 2 Review May 30 and 31, 2013. Acids and Bases 3 Standards 18 Questions."— Presentation transcript:

1 Semester 2 Review May 30 and 31, 2013

2 Acids and Bases 3 Standards 18 Questions

3 Temperature and Thermochemistry 4 Standards 24 Questions

4 Reaction Rates 3 Standards 15 Questions

5 Chemical Equilibrium 2 Standards 10 Questions

6 Biochemistry and Organic Chemistry 2 Standards 10 Questions

7 Nuclear Chemistry 2 Standards 8 Questions

8 (5b) Acids are hydrogen-ion-donating and bases are hydrogen-ion-accepting substances. HCl(g) + H 2 O(l) → H 3 O + (aq) + Cl - (aq) CH 3 COOH(aq) + H 2 O(l) ↔ H 3 O + (aq) + CH 3 COO - (aq) KOH(aq) → K + (aq) + OH - (aq) NH 3 (aq) + H 2 O(l) ↔ NH 4 + (aq) + OH - (aq) Dissociation of a strong acid: Dissociation of a weak acid: Dissociation of a strong base: Dissociation of a weak base: Hint! Dissociate means separate. Acids dissociate to form a conjugate base. Bases dissociate to form a conjugate acid.

9 (5c) Strong acids and bases fully dissociate and weak acids and bases partially dissociate. Strong Acid: All the acid molecules have dissociated to form hydronium (H 3 O + ) and the conjugate base. Weak Acid: Only some of the acid molecules have dissociated to form hydronium (H 3 O + ) and the conjugate base. Other acid molecules remain. Strong Base: All the base molecules have dissociated to form hydroxide (OH - ) and the conjugate acid. Weak Base: Only some of the base molecules have dissociated to form hydroxide (OH - ) and the conjugate acid. Other base molecules remain.

10 (5d) Students know how to use the pH scale to characterize acid and base solutions. The pH scale goes from Water is neutral, and has a pH of 7. Acids have a pH below 7, and bases have a pH above 7. Each value of pH means the concentration of H + changes by a power of 10. Example: pH 1 means [H 3 O + ] = and pH 2 means [H 3 O + ] = As the pH decreases, the hydronium ion concentration [H 3 O + ] increases and the hydroxide ion concentration [OH - ] decreases. As the pH increases, the hydronium ion concentration[H 3 O + ] decreases and the hydroxide ion concentration [OH - ] increases. Most AcidicMost Basic

11 (7a) Describe temperature and heat flow in terms of the motion of molecules (or atoms). Temperature is a measure of the average kinetic (movement) energy of particles in an object. As kinetic energy increases, temperature increases. Because molecular motion increases as a substance changes from solid, to liquid, to gas, temperature increases as well. System: The egg Surroundings: The pan, stove, etc. Heat flows: Into the egg Heat is a form of energy. Heat is transferred from high temperature (hot) to low temperature (cold).

12 (7b) Chemical reactions either release (exothermic) or absorb (endothermic) thermal energy. Endothermic = absorb energyExothermic = release energy Energy or heat (expressed in joules or kilojoules) is a reactant. Endothermic chemical reactions feel cold because heat energy is converted to potential energy. NaCl(s) + H 2 O(l) + energy  NaCl(aq) Li 2 O + H 2 O kJ/mol → 2 LiOH Energy or heat (expressed in joules or kilojoules) is a product. Exothermic chemical reactions fell hot because potential energy is converted to heat energy. KBr(aq) + AgNO 3  AgBr(s) + KNO 3 (aq) + energy 1 H 3 PO HCl → 1 PCl H 2 O kJ/mol

13 (7c) Energy is released when a material condenses or freezes and is absorbed when a material evaporates or melts. Which phase changes are endothermic? Which are exothermic? Does adding heat to water always increase its temperature? Why or why not? What temperatures (C and K) are the melting point, freezing point, and boiling point of water? What parts of the phase change diagram represent a phase change? How do you know?

14 (7d) Solve heat flow and temperature change problems. Multi-Step Thermochemistry Problems: The Basic Steps to Solve: Step 1: Break down the problem into “temperature change” and “phase change” steps. Use the boiling point and melting point as a guide. Step 2: Solve the steps separately. Use q=mcΔT for temperature change and q = mΔH t for phase change Step 3: Add up the answers to get the total heat transferred. Phase Change: Q = m × ΔH tranformation Example Problem: How much heat is absorbed when 100 g of water is heated from 365 K to steam at 400 K? Step 1: The boiling point of water is 373 K ΔT = = 35K phase change = evaporation Step 2: q=mcΔT q = (100g)(4.18J/gK)(35K) q = 14,630 J q = mΔH t q = (100g)(2260J/g) q = 226,000 J Step 3: 14,630 J + 226,000 J = 240,630 J

15 (8a) The rate of reaction is the decrease in concentration of reactants or the increase in concentration of products with time. Reaction rate is the rate at which a chemical reaction takes place. It is measured by the rate of production of product or disappearance of reactant. Usually, the rate decreases gradually as the reaction continues. The rate is zero when the reaction is complete. Rate = change over time Example Test Question C 3 H 8 (g) + 5 O 2 (g) → 3 CO 2 (g) + 4 H 2 O(g) + heat Which is an acceptable method to measure the rate of the reaction? (a) the rate of consumption of C 3 H 8 (b) the rate of consumption of O 2 (c) the rate of production of CO 2 (d) All of the above Can you justify your answer?

16 (8b) Reaction rates depend on such factors as concentration, temperature, and pressure. To start a chemical reaction, molecules must collide with a certain amount of energy. As reactant concentration increases, rate increases. As reactant concentration decreases, rate decreases. As surface area increases, rate increases. As surface area decreases, rate decreases. If working with gases, as pressure increases, rate increases. As pressure decreases, rate decreases. As temperature increases, rate increases. As temperature decreases, rate decreases.

17 (8c) What is the role a catalyst plays in increasing the reaction rate? Activation Energy is the minimum amount of energy required to start a chemical reaction. A catalyst is a substance that increases the reaction rate when it is added to a reaction mixture. Catalysts increase the reaction rate by lowering the activation energy. A catalyst is not a reactant or a product because it is not used up or changed during the reaction. An enzyme is a protein that acts as a catalyst. It is a biological catalyst. The new reaction pathway should have the same “reactants” and “products” energy level. The hill of activation energy should be smaller.

18 (9a) Use Le Chatelier's principle to predict the effect of changes on an equilibrium system. Example #1 exothermic reaction: N 2 (g) + 3H 2 (g) ↔ 2NH 3 (g) + heat Stress on SystemDirection of ShiftReason for Shift Increase temperatureLeft (reverse reaction)Favors endothermic reverse reaction to use up the extra heat Decrease temperatureRight (forward reaction)Favors exothermic forward reaction to produce more heat Add reactantsRight (forward reaction)Increases the forward reaction to change the added reactants into products Add productsLeft (reverse reaction)Increases the reverse reaction to change the added products into reactants Removes reactantsLeft (reverse reaction)Increases the reverse reaction to make more reactants Remove productsRight (forward reaction)Increases the forward reaction to make more products Increase pressureRight (forward reaction)Increases the forward reaction because there are 2 moles of products, taking up less space than 3 moles of reactants Decrease pressureLeft (reverse reaction)Increases the reverse reaction because the decrease in pressure creates more room for the 3 moles of reactants Le Chatelier’s Principle: For a reversible process at equilibrium, when conditions of concentration, temperature, or pressure are changed, the reaction shifts in a direction that will counteract the stress and restore equilibrium.

19 (9a) Use Le Chatelier's principle to predict the effect of changes on an equilibrium system. Example #1 endothermic reaction: N 2 O 4 (g) + heat ↔ 2NO 2 (g) Stress on SystemDirection of ShiftReason for Shift Increase temperatureRight (forward reaction)Favors endothermic forward reaction to use up the extra heat Decrease temperatureLeft (reverse reaction)Favors exothermic reverse reaction to produce more heat Add reactantsRight (forward reaction)Increases the forward reaction to change the added reactants into products Add productsLeft (reverse reaction)Increases the reverse reaction to change the added products into reactants Removes reactantsLeft (reverse reaction)Increases the reverse reaction to make more reactants Remove productsRight (forward reaction)Increases the forward reaction to make more products Increase pressureLeft (reverse reaction)Increases the reverse reaction because there is 1 mole of reactants, taking up less space than 2 moles of products Decrease pressureRight (forward reaction)Increases the forward reaction because the decrease in pressure creates more room for the 2 moles of products Le Chatelier’s Principle: For a reversible process at equilibrium, when conditions of concentration, temperature, or pressure are changed, the reaction shifts in a direction that will counteract the stress and restore equilibrium.

20 (9b) Equilibrium is established when forward and reverse reaction rates are equal. Chemical equilibrium is a state of balance in which the rate of a forward reaction equals the rate of the reverse reaction and the concentrations of the products and reactants stop changing. The amounts of products and reactants do not have to be equal. Only reversible chemical reactions can reach equilibrium. Reversible reactions are shown with a double arrow: Ex: H 2 SO 4  2H + + SO 4 2 When this reaction is in equilibrium, H 2 SO 4 is produced and broken down at equal rates. Example Problems: 2N 2 (g) + 6 H 2 O (l)  4NH 3 (g) + 3O 2 (g) 1) Write the forward reaction: 2N 2 (g) + 6 H 2 O (l)  4NH 3 (g) + 3O 2 (g) 2) Write the reverse reaction: 4NH 3 (g) + 3O 2 (g)  2N 2 (g) + 6 H 2 O (l) 3) At equilibrium, does the concentration of water have to equal the concentration of oxygen? Answer: No, the concentrations of products and reactants do not have to match. But, the rate of the forward and reverse reactions will be the same.

21 (10a) Polymers are made of repetitive combinations of simple subunits. MacromoleculePolymerMonomer ProteinPolypeptideAmino acid CarbohydratepolysaccharideMonosaccharide Nucleic acidDNA/RNAnucleotide Lipid - not polymers because they are not long chains Hydrolysis reactions break down polymers into monomers Condensation reactions connect monomers to make a polymer

22 (10b) Carbon’s bonding characteristics allow it to form a large variety of structures. Carbon has four valence electrons. Because carbon can form simultaneous covalent bonds with up to four partners, an enormous number of carbon compounds are possible. Among the simplest organic compounds are those containing only hydrogen and carbon, or hydrocarbons. Hydrocarbons include methane gas, liquid gasoline, and solid paraffin wax in candles. Carbon is the backbone of the macromolecules also. Allotropes of carbon are diamond, graphite, and graphene. The different carbon structures lead to different properties.

23 (11c) Radioactive isotopes may be man-made or found in nature. Radioactivity is the spontaneous changing of the nucleus of an atom from one element to another. Radioactive isotopes occur naturally. They are also man-made. Half-Life is the amount of time it takes for ½ of a radioactive substance to undergo radioactive decay. Example: The half-life of Carbon-14 is 5700 years. A sample containing 100 g of carbon-14 today, will contain 50 g carbon-14 in 5700 years from now. Nuclear fission is the process of splitting the nuclei of atoms, which releases energy from within those atoms. Nuclear fusion is the process of joining, rather than splitting, such atomic particles with similar releases of energy.

24 (11c) The three most common types of nuclear decay are alpha, beta, and gamma. Each changes the nucleus in a different way Po He Pb Pb 82 Alpha (α) decay: The mass number decreases by 4 and the atomic number decreases by C e N 7 14 N 7 Beta (β) decay: The mass number remains the same. The atomic number increases by Cr + e + γ V V 23 Gamma (γ): Gamma rays are released during electron capture.


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