CHEM 1010 CH 9
According to the following balanced chemical equation, if you want to generate two moles of H2O, how many moles of O2 do you need? 2 H2 + O2 → 2 H2O 1 4 6.022 × 1023 1/2 2
A
How many grams of water can be formed from the reaction between 10 grams of oxygen and 1 gram of hydrogen? 9 grams of water are formed because oxygen and hydrogen react in an 8:1 ratio. No water is formed because there is insufficient hydrogen to react with the oxygen. 10 grams of water are formed since you can't get a greater mass of water produced than oxygen reacting. 11 grams of water are formed since mass must be conserved.
A
In a chemical equation the coefficients ________. - appear before the chemical formulas - of the reactants should always sum up to those of the products - appear as subscripts - More than one of the answers are correct.
A
In the laboratory, endothermic reactions are usually performed at elevated temperatures, while exothermic reactions are usually performed at lower temperatures. Why? - All of the reasons are correct. - Performing endothermic reactions at elevated temperature gives the molecules greater kinetic energy. Also, some exothermic reactions would explode if not run at cold temperatures. - Endothermic reactions require the input of energy, which can include the input of thermal energy. Elevated temperatures help minimize unfavorable decrease in entropy due to the heat absorbed by the reaction. - For exothermic reactions, the lower temperatures slow the reactive molecules down, which gives the chemist greater control. Also, the heat generated by the reaction is more efficiently dispersed under the colder conditions.
A
The ________ is what needs to be overcome in a reaction so that it can proceed to the products. activation energy catalyst bond energy thermodynamics entropy
A
What is the number of moles of H2O produced if you combust one mole of CH4 according to the following balanced equation? CH4 + 2 O2 → CO2 + 2 H2O 2 moles 6 moles 8 moles 4 moles 1 mole
A
Which has more atoms: 17.031 g of ammonia, NH3 (17.031 amu), or 72.922 g of hydrogen chloride, HCl (36.461 amu)? 72.922 g of HCl has more atoms than 17.031 g of NH3 Not enough information is given. 17.031 g of NH3 has more atoms than 72.922 g of HCl 72.922 g of HCl and 17.031 g of NH3 have about the same number of atoms.
A
Which has more atoms: 64.058 g of sulfur dioxide, SO2 (64.058 amu), or 72.922 g of hydrogen chloride, HCl (36.461 amu)? 72.922 g of HCl has more atoms than 64.058 g of SO2 Not enough information is given. 64.058 g of SO2 has more atoms than 72.922 g of HCl 72.922 g of HCl and 64.058 g of SO2 have about the same number atoms.
A
Which has the greatest number of molecules? 32 g of methane, CH4 38 g of fluorine, F2 32 g of oxygen, O2 28 g of nitrogen, N2
A
Which of the following statements is not in line with the concepts of thermodynamics? -Energy has a tendency to stay in one place. - All of the above describe the concepts of thermodynamics. - The entropy of the universe is constantly increasing. - The energy released in a chemical reaction is the same as the difference in the energy of the bonds broken and formed. - Energy is neither created nor destroyed.
A
Why might increasing the concentration of a set of reactants increase the rate of reaction? - You have increased the chances that any two reactant molecules will collide and react. - The concentration of reactants is unrelated to the rate of reaction. - You have increased the ratio of reactants to products. - The rate of reaction depends only on the mass of the atoms and therefore increases as you increase the mass of the reactants.
A
How does a catalyst increase the rate of a reaction? - It increases the energy difference between the reactants and products. - It lowers the activation energy. - It raises the activation energy of the reactants, which makes the reaction proceed faster. - It has nothing to do with the rate of reaction.
B
How many total bonds between nitrogen and hydrogen are formed if you react nitrogen with hydrogen according to the following reaction? N2 + 3H2 → 2 NH3 3 6 1 2 8
B
How much energy, in kilojoules, is released or absorbed from the reaction of one mole of nitrogen, N2, with three moles of molecular hydrogen, H2, to form two moles of ammonia, NH3? H-N (bond energy: 389 kJ/mol) H-H (bond energy: 436 kJ/mol) NN (bond energy: 946 kJ/mol) NN + H-H + H-H → NH3 + NH3 -993 kJ/mol released -80 kj/mol released +899 kJ/mol absorbed +80 kJ/mol absorbed
B
If the relative mass of a hydrogen atom is 1/4 that of a helium atom, how many hydrogen atoms would you need to equal the mass of four helium atoms? 25 16 6.022 × 1023 4 1/4
B
In a chemical equation the coefficients ________. - appear as subscripts - appear before the chemical formulas - More than one of the answers are correct. - of the reactants should always sum up to those of the products
B
What is a reaction rate? - It is the balanced chemical formula that relates the number of product molecules to reactant molecules. - It is the speed at which reactants are consumed or product is formed. - It is the ratio of the molecular masses of the elements in a given compound. - It is the ratio of the masses of products and reactants.
B
What is an exothermic reaction? It is a reaction that requires heat as a reactant. All of the answers are correct. None of the answers are correct. It is a reaction where the products have more energy than the reactants. It is a reaction where there is a net adsorption of energy from a reaction.
B
What is the formula mass of sulfur dioxide, SO2? about 60 amu about 64 amu about 16 amu about 32 amu
B
Entropy is a measure of ________. - thermodynamics - solar energy - the spreading of energy, sometimes described as disorder - chemical potential energy
C
Given the following energy profiles, which of the following reactions is endothermic? >v >v .>v ^> . R= reactants P= products b a d c
C
How many grams of water, H2O, and propene, C3H6, can be formed from the reaction of 6.0 g of 2-propanol, C3H8O? C3H8O → C3H6 + H2O 2-Propanol Propene Water 1.8 grams of propene, 4.2 grams of water 6.0 grams of propene, 0.0 grams of water 4.2 grams of propene, 1.8 grams of water 0.0 grams of propene, 6.0 grams of water
C
What can you deduce about the activation energy of a reaction that takes billions of years to go to completion? How about a reaction that takes only fractions of a second? - The activation energy of both these reactions must be very high. - The slow reaction must have a low activation energy while the fast reaction must have a high activation energy - The slow reaction must have a high activation energy while the fast reaction must have a low activation energy. - The activation energy of both these reactions must be very low.
C
What is an exothermic reaction? -It is a reaction where there is a net adsorption of energy from a reaction. - All of the answers are correct. - None of the answers are correct. - It is a reaction where the products have more energy than the reactants. - It is a reaction that requires heat as a reactant.
C
What is the formula mass of a molecule of CO2? 118 amu 58.9 amu 44 amu 56 amu
C
What is the mass of an oxygen atom, O, in atomic mass units? 18 amu 32 amu 16 amu 12 amu
C
Which of the following has the greatest number of particles? 1 mole of Be 1 mole of Na All have the same number of particles. 22.990 g of Na 9.012 g of Be
C
According to the following balanced chemical equation, if you want to generate two moles of H2O how many grams of O2 do you need? 2 H2 + O2 → 2 H2O 16 8 6.022 × 1023 32
D
Assume air has an average molar mass of 28 grams/mole, and determine how many moles of air molecules there are 1.0 liters of air, which contains 1.26 grams of air molecules. 0.45 mole 28 moles 22.4 moles 0.045 mole
D
Balance the following chemical equation. ____ N2 + ____ H2 → ____ NH3 3, 2, 1 1, 2, 3 2, 6, 4 1, 3, 2
D
Carefully examine the following reaction sequence for the catalytic formation of ozone, O3, from molecular oxygen, O2. Which chemical compound is behaving as the catalyst? O2 + 2 NO → 2 NO2 2 NO2 → 2 NO + 2 O 2 O + 2 O2 → 2 O3 Nitrogen dioxide, NO2 Oxygen, O2 Atomic oxygen, O Nitrogen monoxide, NO
D
Given the following generic chemical reaction, which is the reactant? X → Y] Both X and Y are the reactants. Both X and Y are the products. → is the reactant. X is the reactant. Y is the reactant.
D
How many oxygen molecules are needed to make 10 carbon dioxide molecules according to the following balanced chemical equation? 2 CO + O2 → 2 CO2 4 10 2 5 1
D
If it takes 200 golf balls to equal the mass of four bowling balls, what is the relative mass of bowling balls to golf balls? 1/20 20 times 6.022 × 1023 1/50 100 times
D
If it takes energy to break bonds and you gain energy in the formation of bonds, how can some reactions be exothermic while others are endothermic? -Some reactants have more energetic bonds than others and they will always release energy. -It is the total number of bonds that matters. ---- -Sometimes you create more bonds than you break and since all bonds have same amount of energy you gain or lose energy depending on the number of bonds. -Some products have more energy than others and they always require energy to be formed. - It is the net amount of energy that is absorbed or released that determines whether the reaction is endothermic or exothermic.
E
Which of the following statements about catalysts is NOT true? - A catalyst does not change the energy of the reactants or the products. - A catalyst can be consumed in a reaction as long as it is regenerated. - A catalyst alters the rate of a chemical reaction. - A catalyst can be used to speed up slow reactions. - All of the statements about catalysts are true.
E
