Semester 2 Review

Stoichiometry Convert from one substance to another. Convert from one substance to another. Determine amount of reactant/product Determine amount of reactant/product Determine limiting reactant/excess Determine limiting reactant/excess Determine theoretical & percent yield Determine theoretical & percent yield Use density to convert between substances. Use density to convert between substances.

Using the following balanced chemical reaction: CH 4 (g) + 2O 2 (g)  CO 2 (g) + 2H 2 O(g) How many molecules of oxygen are needed to react with 24.5 g of CH 4 ? 1.83 x molecules O 2

What volume of hydrogen gas is produced if there are 112 g NH 3 in the following reaction? (The density of hydrogen is 8.90 x g/L) 2 NH 3 (g)  N 2 (g) + 3H 2 (g) 224 L

If reactant “A” runs out before reactant “B” and the reaction stops, then reactant “A” is know as the … LIMITING REACTANT

Using the following reaction, 2Na(s) + 2H 2 O(g)  2NaOH(aq) + H 2 (g) If you have 15.2 g of Na and 12.5 g of H 2 O, how many grams of H 2 gas can be made? g H 2

If the theoretical yield of a reaction is 125 g and the actual yield is 115 g, what is the percent yield? 92.0 %

States of Matter and Intermolecular Forces Identify polar and nonpolar molecules. Identify the types of intermolecular forces. Determine low/high melting and boiling point using intermolecular forces.

Which have higher melting and boiling points, polar substances or non-polar substances? Polar Why? Dipole-Dipole intermolecular forces are harder to break (take more energy) than dispersion forces.

Describe each of the three intermolecular forces. Dispersion forces… Weakest intermolecular force. Temporary attractions (dipoles) between the electron cloud of one NONPOLAR molecule to the nucleus of a nearby molecule. Dipole - Dipole forces… Attraction between the permanent negative dipole on one molecule to the permanent positive dipole on a nearby molecule. Hydrogen Bonds Strongest intermolecular force. A hydrogen (bonded to a very electronegative N, O, or F) is attracted to the highly negative N, O, or F of a nearby molecule.

GASES STP values Use gas laws to determine pressure, volume, and temperature. Use gas laws to determine moles or grams or molar mass. Use gas laws and stoich. to determine amounts of reactants and products.

What are STANDARD conditions for gases? 0 o C or 273K and 1 atm pressure

A sample of gas has a volume of 25 mL and a temperature of 65 o C. What will the volume be if the temperature is raised to 125 o C? 29 mL

How many grams of gas are present in a sample that has a molar mass of 70.0 g/mol and occupies 2.00 L at 117 kPa and 35.1 o C? 6.36 g

Ideal gas and Molar Mass At 28 o C and atm, 1.00 L of gas has a mass of 5.16 g. What is the molar mass of this gas? At 28 o C and atm, 1.00 L of gas has a mass of 5.16 g. What is the molar mass of this gas? Answer: 131 g/mol Answer: 131 g/mol

Calculate the mass of solid ammonium nitrate that must be used to obtain L of dinitrogen monoxide gas at STP. NH 4 NO 3 (s)  N 2 O(g) + 2H 2 O(g) g

Solutions Solubility (“like dissolves like”) Concentration (molarity) Vocab unsaturated, saturated, supersaturated, soluble, insoluble, miscible, immiscible Colligative Properties Electrolytes and Non-Electrolytes

What is the molarity of a 500. mL solution that contains 125 g of sodium hydroxide? 6.25 M

How many milliliters of a M solution of sodium thiosulfate, Na 2 S 2 O 3, contain mol of Na 2 S 2 O 3 ? L

What is soluble in water Identify which of the following substances is/are soluble in water: Identify which of the following substances is/are soluble in water: Aluminum - Al Aluminum - Al CaCl 2 CaCl 2 C 3 H 8 C 3 H 8 CCl 4 CCl 4 CaCl 2

For which type of substances does an increase in pressure increase solubility? GASES

Define the following terms: Saturated: Unsaturated: Supersaturated: The maximum amount of solute that can dissolve in a given amount of solvent. Less than the maximum amount of solute that can dissolve in a given amount of solvent. More than the maximum amount of solute is dissolved. The substance must be heated, more solute added, and then cooled.

Which of the following solutions will have the highest boiling point? 1.0 M C 2 H 5 OH (ethanol) 1.0 M C 2 H 5 OH (ethanol) 1.0 M KCl 1.0 M KCl 1.0 M FeCl M FeCl 3 Pure water Pure water 1.0 M FeCl 3

Rates Collision Theory What affects rate? Concentration, surface area, temp How does rate change over time and why? Catalysts

Describe collision theory Reactants must collide (with enough energy and the correct orientation) in order to produce an activated complex and form product. Reactants must collide (with enough energy and the correct orientation) in order to produce an activated complex and form product.

How does a catalyst increase the rate of a reaction? It lowers the activation energy by creating an alternate path.

How does the rate of a reaction change over time? The rate slows down because the concentration of the reactants decreases over time.

Equilibrium Completion vs. Reversible Rates of reactions at equilibrium K (what does big vs. small mean) LeChatelier’s Principle Equilibrium expressions Calculating K Ksp

Equilibrium Expressions Write the equilibrium constant for the following reaction: N 2 (g) + 3 H 2 (g)  2 NH 3 (g) [NH 3 ] 2 [N 2 ][H 2 ] 3 = Keq

2 NO 2 (g)  N 2 O 4 (g) + Energy What happens if we… Lower the Temperature Lower the Temperature Increase N 2 O 4 Increase N 2 O 4 Decrease NO 2 Decrease NO 2 Increase Pressure Increase Pressure Increase Volume Increase Volume Shift right Shift left Shift right Shift left

What does it mean if the reaction shifts to the right? How would the amounts of reactants and products change? Amounts of reactants decrease and products increase.

Acids and Bases Electrolytes and Strong vs. Weak Bronsted – Lowry Amphoprotic – Amphoteric pH calculations Titrations(Buffer)

Label the A, B, CA, CB in the following reaction: HSO 4 - (aq) + H 2 O (l)  H 3 O + (aq) + SO 4 2- HSO 4 - (aq) + H 2 O (l)  H 3 O + (aq) + SO 4 2- A B CA CB A B CA CB

Strong acids and bases ionize ___________ while weak acids and bases ionize __________. completely, partially completely, partially

What word is used to describe substances that can act as an acid or a base? Answer: Amphoteric

What is the concentration of H+ if the pOH is 7.82? 6.61 x M

What is the pH of M HCl (a strong acid)? Answer: 3.60

A student titrates 40.0 mL of an H 2 SO 4 solution of unknown concentration with mL of a M NaOH solution. What is the molarity of the H 2 SO 4 solution? [HCl] = M

Acc Only! A buffer is a mixture of what 2 substances? Weak acid and its conjugate base Or Weak base and its conjugate acid

Thermochemistry Exo vs. Endo EnthalpyEntropy Free Energy

For each of the following phase changes, determine if they are endothermic or exothermic. Melting Melting Freezing Freezing Subliming Subliming Endothermic Endothermic Exothermic Exothermic Endothermic Endothermic

At low temperatures, is entropy or enthalpy more important in determining spontaneity? Enthalpy

For a reaction at 298K,  H = -235 kJ/mol and  S = 98 J/K. What is the value of  G and is the reaction spontaneous? -264 kJ and it is spontaneous

In nature, processes that happen spontaneously tend to have what signs (+ or -) for  H and  S? -  H and +  S

For endothermic reactions, which has more energy, the reactants or the products? Products