The Chemistry Workshop   

The Chemistry Workshop      Ungrouped Chemistry Homework for the weeks of 4/27 & 5/4

Monday, 4/27--Complete the Chapter 8 Calculations Party Too Handout

Tuesday, 4/28--Chapter 8 exam

This is a calculations exam with 9 questions--one period exam.

--Be able to determine the Molar Mass of a compound (see sample problem 8h)

--Be able to calculate % Composition from the formula of a compound (see sample problem 8l)

--Be able to determine the Empirical Formula of a compound from % composition data (see sample problem 8j)

--Be able to determine the Molecular Formula of a compound from empirical formula data (see sample problem 8k)

--Be able to convert from mass to moles for a compound (see sample problem 8e)

--Be able to convert from moles to mass of a compound (see sample problem 8d)

--Be able to calculate the number of atoms or molecules if given the number of moles or the mass (see sample problem 8a)

--Be able to calculate the mass or number of moles if given the number of atoms or molecules (see sample problem 8b)

Tuesday, 4/28--Read 9-1 and answer these questions.

1.  Define or describe these chapter 9 terms:  Chemical Reaction, Reactants, Products

2.  Compare the materials you have before a chemical reaction to those you have after a chemical reaction has occurred.

3.  Describe the changes that you can observe when a match burns.

4.  Study figure 9-2.  What can be observed in this image?

5.  How can you tell the difference between a physical change and a chemical change?

6.  In a chemical reaction, you have the same atoms at the end as you had in the beginning, so what changed?

7.  List 4 observations that signify a that a chemical change might be taking place.

8.  What proves that a chemical change has occurred?

Wednesday, 4/29--Read 9-1 and answer these questions.

9.  Why are heat, light, and sound indicators that a chemical reaction has taken place?

10. Explain the difference between an exothermic and an endothermic chemical reaction.

11. What is a spontaneous reaction?

12. (a) Look at the reaction of iron and oxygen on page 310.  Where does the book place energy in this reaction? 

(b) Is this an exothermic or endothermic reaction?

13. (a) Look at the reaction of dinitrogen pentoxide on page 310.  Where does the book place energy in this reaction? 

(b) Is this an exothermic or endothermic reaction?

14. Study figure 9-3. (a) What does this image show?     (b) What are the bubbles?      (c) What does the battery do?

(d) Is this reaction endothermic or exothermic?  EXPLAIN.

15. (a) What is required to break chemical bonds?      (b) What happens when chemical bonds form?     (c) In an exothermic reaction, how do the bonds holding the reactants together compare to the bonds holding the products together?  Explain.

Thursday, 4/30--Read 9-1 and answer these questions.

16. Explain how (a) molecular collisions and (b) collision energy determine if a chemical reaction will occur or not.

Section 9-1 Review:

17. What is a chemical reaction?

18. What is the only way to prove that a chemical reaction has occurred?

19. In an exothermic reaction, are the bonds in the products stronger or weaker than the bonds in the reactants?

20. In an exothermic reaction, are the bonds in the products higher or lower in energy than the bonds in the reactants?

21. At what point will a spontaneous reaction stop?

22. Do you think the burning of gasoline in a car's engine is exothermic or endothermic?  Explain

Friday, 5/1 & over the weekend--Chapter 9-1 Review

23. What is the role of collisions in chemical reactions?

24. Do you think fireworks exploding in the sky are exothermic or endothermic?  Explain.

25. When an orange compound is heated, it reacts by giving off nitrogen gas, green crystals of chromium(III) oxide, and water vapor.  What elements were in the original compound?

26. (a) Is the description given in question 22 a chemical change or a physical change?     (b) How do you know?

27. (a) Is the description given in question 24 a chemical change or a physical change?     (b) How do you know?

28. (a) Is the description given in question 25 a chemical change or a physical change?     (b) How do you know?

29. Calcium Oxide, CaO, is an ingredient in cement mixes.  When water, H₂O is added, CaO reacts in an exothermic reaction to form calcium hydroxide, Ca(OH)₂.  The properties of CaO are different from the properties of Ca(OH)₂.

        (a) Write out this chemical reaction.  I gave you the formulas, put them in the form of a chemical reaction.

        (b) Are the bonds stronger in the reactants or the products?  Explain.

        (c) Is there any evidence that a chemical reaction actually occurred?  Explain.

Monday, 5/4--Read 9-2 and answer these questions.

30. (a) What is a Chemical Equation?     (b) How are word equations and formula equations different?

31. (a) Why must chemical equations be balanced?     (b) What are the numbers you put in front of the formulas called?

32. Write down the "Tips For Balancing Equations" found on page 315.

33. Study Sample Problem 9a.  Then balance these equations:

      (a) ZnS  +  O₂  ==>  ZnO  +  SO₂

      (b) CS₂  +  O₂  ==>  CO₂  +  SO₂

      (c) C₂H₂  +  O₂  ==>  CO₂   +  H₂O

      (d) N₂O₅  +  NO  ==>  NO₂

Tuesday, 5/5--Read 9-2 and answer these questions.

34. Explain why, when balancing an equation, you can only add coefficients, but you NEVER change the subscripts.

35. Write the following as formula equations.  Then balance each one:

        (a) Hydrogen gas + Chlorine gas react to produce hydrogen chloride.  (Note: both hydrogen gas and chlorine gas are diatomic)

        (b) Aluminum metal + iron (III) oxide react to produce aluminum oxide and iron metal.

        (c) Potassium chlorate decomposes to form potassium chloride and oxygen gas.  (Note: oxygen gas is diatomic)

        (d) Calcium hydroxide and hydrochloric acid react to form calcium chloride and water.

36. Balance the following reactions:

      (a) CaSi₂  +  SbCl₃  ==>  Si  +  Sb  +  CaCl₂                         (c) Al  +  CH₃OH  ==>  (CH₃O)₃Al  +  H₂

      (b) P₄  +  O₂  ==> P₂O₅                                                       (d) Fe  +  O₂  ==>  Fe₂O₃

Wednesday, 5/6--Read 9-3 and answer these questions.

37. (a) How is a chemical equation like a cooking recipe?     (b) How is it unlike a cooking recipe?

38. Study Table 9-5.  List the 6 things written above the arrow of a chemical reaction and what they stand for.

39. Study Table 9-6.  List the 6 ways of indicating the physical state of reactants and products and what they stand for.

40. Study Table 9-7.  Balance the reaction CH₄  +  O₂  ==>  CO₂  +  H₂O.  Interpret this reaction...

        (a) From a mole perspective.     (b) From a mass perspective.     (c) From a molecule perspective

41. In the balanced reaction from question 40, what is the mole ratio between...

      (a) CH₄ and O₂     (b)  CH₄ and CO₂     (c) CH₄ and H₂O     (d) O₂ and CO₂     (e) O₂ and H₂O     (f) CO₂ and H₂O

42. Use the balanced equation from question 40 to...

        (a) Calculate the number of moles of CO₂ produced when 2.5 moles CH₄ is burned.

        (b) How much CH₄ must be burned to produce 5.6 moles of water?

Thursday, 5/7--Read 9-3 and answer these questions.

43. (a) When a reaction is endothermic, what side of the reaction could energy be written on?

        (b) When a reaction is exothermic, what side of the reaction could energy be written on?

44. What are the units of energy?

45.  Define Enthalpy.

46. Consider this reaction: 2 Al  + 3 Br₂  ==> 2 AlBr₃  +  1055 KJ

        (a) Is this reaction exothermic or endothermic?                     

        (b) How much energy is released per mole of bromine used?

        (c) How much energy is released per mole of aluminum used?

        (d) How much energy is released per mole of aluminum bromide made?

47. (a) How big is a joule?

        (b) How big is a Kjoule?

        (c) How many calories should an "average" female consume each day?

        (d) If 1 calorie = 4.184 joules, CALCULATE how many joules an "average" female should consume each day.

        (e) How many calories should an "average" male consume each day?

        (f) If 1 calorie = 4.184 joules, CALCULATE how many joules an "average" male should consume each day.