The law of conservation of energy

1) The law of conservation of energy states that ________.

A) the energy of the reactants and products in a chemical reaction are always equal

B) all chemical reactions are reversible

C) energy can be created, but not destroyed

D) energy cannot be created or destroyed

2) Which of the following energy quantities is equivalent to 578 J?

A) 5.78 × 105 kJ                                 C) 0.138 kcal

B) 138 kcal                                           D) 1.38 × 105 kcal

3) Which of the following energy quantities is equivalent to 11.9 kcal?

A) 1.19 × 105cal                 C) 49.8 kJ

B) 49.8 J                                                D) 2.84 × 103 kJ

4) Which of the following energy quantities is equivalent to 258 Cal?

A) 258 cal                                             C) 1080 kJ

B) 1080 J                                               D) 6.17 × 104 kJ

5) Which quantity represents the largest amount of stored energy?

A) 10 grams of fat

B) 10 grams of carbohydrate

C) 10 grams of protein

D) 5 grams of carbohydrate plus 5 grams of protein

E) 5 grams of protein plus 5 grams of fat

6) Which bond is the strongest?                                                                                                                

A) H–Br                                                                C) H–F

B) H–Cl                                                 D) H–I

7) Which bond is the weakest?

A) H–Br                                                                C) H–F

B) H–Cl                                                 D) H–I

8) Which term correctly describes a reaction in which the energy of the products is higher than the energy of the reactants?

A) Oxidation-reduction                 C) Exothermic

B) Endothermic                                 D) Combustion

9) Consider the reaction: C3H8(g) + 5 O2(g) → 3 CO2(g) + 4 H2O(g), where ΔH = –531 kcal. Which statement concerning this reaction is true?

A) Heat is absorbed.

B) The bonds formed in the products are stronger than the bonds broken in the reactants.

C) The products are higher in energy than the reactants.

D) The reaction is endothermic.

Short Answer / Problem Solving (Show your work):

10) A chemical reaction requires 31.39 kJ. How many kilocalories does this correspond to?

11) A peanut butter and jelly sandwich contains 9.00 g of fat, 6.00 g of protein, and 25.0 g of carbohydrate. How many Calories does this sandwich provide?

12) Consider the reaction, C2H4(g) + H2(g) → C2H6(g), where ΔH = –137 kJ. How many kilojoules are released when 3.5 mol of C2H4 reacts?

13) Consider the reaction, C2H4(g) + H2(g) → C2H6(g), where ΔH = –137 kJ. How many kilojoules are released when 55.3 g of C2H4 reacts?

14)  Watch the following video and complete the calculation to determine the specific heat of the cadmium metal:  https://www.youtube.com/watch?v=8gHFaL2990U