Chemistry Quarter 3 Assessment Review

Stoichiometry

1.Butane reacts with oxygen according to the reaction given below. a.What is the mole ratio between butane and oxygen? b.How many moles of C 4 H 10 are needed to fully react 26 moles of O 2 ? OR Mole Ratio: always between moles in a balanced equation

Stoichiometry 1.Butane reacts with oxygen according to the reaction given below. c.How many moles of O 2 are needed to react with 10 grams of C 4 H 10 ? d.What mass of H 2 O can be obtained from burning 15 grams of C 4 H 10 ?

Stoichiometry 1.Butane reacts with oxygen according to the reaction given below. e.How many liters of CO 2 are produced from 6.5 moles of O 2 ?

Solutions

2.Provide an example of a solution, a suspension, and a colloid. SolutionColloidSuspension Hetero or homogenous? HomogenousHeterogeneous Relative particle size and type Marble, atoms or ionsBaseball, molecules Basketball, Large aggregates Pass through a fine membrane Yes – small enoughNo – too large Pass through a filter Yes – small enough No – too large Settle over time No – water holds up small particles Yes – large particles sink Tyndall effect observed? No – too small to scatter light Yes – large enough to scatter light Example Sugar cube in glass of water MilkMuddy water

Solutions 3.How many moles of NaCl are required to make 0.25 L of a 0.50 M solution? 4.Three liters of solution are prepared using 9 moles of NaOH. What is the molarity of the solution?

Solutions 5.How many mL of 12 M HCl are needed to prepare 100 mL of 2 M HCl?

Solutions 6.Provide an example of a strong, weak, and non-electrolyte. TypeDefinitionExample Strong Electrolyte Dissociates 100% in water Ionic compounds: NaCl, K 2 SO 4 Strong acids: HCl Weak Electrolyte Dissociates much less than 100% in water Weak acids: HC 2 H 3 O 2 (acetic acid) Non Electrolyte Does not dissociate OR contains no ions Hydrocarbons: C 6 H 12 No Ions!

Solutions 7.Define the following: a.Unsaturated solution – Additional solute would still dissolve in the solution b.Saturated solution – Solution contains as much solute possible under the current conditions; no more solute will dissolve if added c.Supersaturated solution – Solution that exceeds its predicted solubility at a certain temperature and pressure – To create a supersaturated solution: Grind up the solute into a powder and heat the solution to make it dissolve

Solutions 8.Draw a picture that shows the interaction between water molecules and NaCl(aq). Na +1 Cl -1 Na +1 NaCl(s) NaCl(aq) Na +1 Cl -1 H O H δ+δ+ δ-δ- H O H δ+δ+ δ-δ- H O H δ+δ+ δ-δ- H O H δ+δ+ δ-δ- H O H δ+δ+ δ-δ- H O H δ+δ+ δ-δ- H O H δ+δ+ δ-δ- H O H δ+δ+ δ-δ- H O H δ+δ+ δ-δ- Na +1 H O H δ+δ+ δ-δ- H O H δ+δ+ δ-δ- H O H δ+δ+ δ-δ-

Solutions 9.Use the solubility curve to answer the following. a.Which compound’s solubility decreases the most as the temperature increases from 50°C to 70°C? – Solubility of gases decrease as temperature increases – Steepest slope = most decrease – NH 3 b.One hundred grams of water are saturated with KNO 3 at 60°C. If the solution cools to 10°C, how much solid KNO 3 will precipitate? 60°C: 110 grams 10°C: 20 grams 90 grams will precipitate

Solutions 9.Use the solubility curve to answer the following. c.Sketch a graph that shows the relationship between solubility and temperature for most solids (such as CaCl 2 ) in water. Temperature Solubility For most solids, as temperature increases, solubility increases

Thermodynamics

10.Consider the enthalpy diagram below. a.What is the heat of reaction, ΔH, for this reaction? – Difference between products and reactants – 50 kJ kJ = -100 kJ b.Make a claim about if the reaction is endothermic or exothermic. Support your claim with evidence. – Exothermic: the reactants are higher than the products, meaning heat must be given off ∆H= -100 kJ

Thermodynamics 10.Consider the enthalpy diagram below. c.What is the activation energy, E a, for this reaction? – Reactants to the top of the hill – 200 kJ – 150 kJ = 50 kJ d.Compare the stabilities of the products and the reactants. – Higher energy = less stable – Reactants are less stable than the products because they are higher energy. E a = 50 kJ

Thermodynamics 11.Provide an example of a phase change that is endothermic and one that is exothermic. – Endothermic: any phase change that requires the substance to absorb heat – Melting – Boiling – Exothermic: any phase change that releases heat/ cools the substance – Freezing – Condensing

Thermodynamics 12.Consider the reaction below. a.What is the ∆H of the reaction? b.Is the reaction endothermic or exothermic? How do you know? – The reaction is endothermic because heat is a reactant. In other words, heat must be absorbed for the reaction to occur. This means that ∆H is positive. c.How many grams of N 2 are required to absorb 156 KJ of energy?

Thermodynamics 13.Entropy is a measure of the disorder of a system. For each of the following, determine if the disorder of the system is increasing or decreasing. a.Ice melts into a liquid – Increase b.Methane crystallizes into a solid – Decrease c.Solid iodine sublimes into a gas – Increase d.Water condenses on a cold can – Decrease

Thermodynamics 14.Consider the pictures below. Explain the direction of heat flow between the blocks. Explain the direction of heat flow between the water and the ice. Heat flows from warmer object to cooler object. Heat will flow from the 200°C block to the 100°C block until both are at the same temperature. Heat exchange will then continue, but equally in each direction. Heat flows from warmer object to cooler object. The water is warmer than the ice, so the ice will absorb heat from the water, melting the ice and cooling the water down.

Thermodynamics 15.In the reaction O 2 + energy  O + O, bonds are being (circle one: broken/ formed) and energy is (circle one: released/ absorbed). + energyOO  OO+

Thermodynamics 16.Using the word bank, label the heating curve below. Word Bank  Solid  Liquid  Gas  Melting Point  Freezing Point  Boiling Point  Condensation Point  Phase Change Solid Liquid Gas Melting Point/ Freezing Point Boiling Point/ Condensation Point Phase change occurs where graph is flat!

Thermodynamics 16.Heating Curve and Data. a.Based on the data, what is the melting point? The boiling point? – Melting Point: 1 st flat part, 5°C – Boiling Point: 2 nd flat part, 60°C b.Which segment of the graph has the most kinetic energy? The least? – Most: Gas; particles are moving the fastest and have the highest temperature – Least: Solid; particles are vibrating in place and have the lowest temperature c.Explain why the temperature remains constant during a phase change. – Heat is still being added, but the temperature remains constant. The added heat is instead being used to break apart the intermolecular attractions that are holding the substance together in that phase (i.e. as a solid) Time (Min)Temperature (°C)