Question

1. some physical properties of two samples of iodine - 127 at two different temperatures are shown in the table below. these two samples are two different a) mixtures b) substances c) phases of matter d) isotopes of iodine 2) a student observed that the temperature of water increased when magnesium metal reacts with it. the student should conclude that reacting water with magnesium a) creates new energy b) reduces thermal energy c) an exothermic reaction d) an endothermic reaction 3) a phase change for carbon dioxide that occurs spontaneously at 20.°c and 1.0 atmosphere is represented by the balanced equation co₂(s) + energy → co₂(g). use the key to draw at least five molecules in the box to represent co₂ after this phase change is completed. 4) given the reaction: iron combines with sulphur to produce iron sulphide and heat energy. which statement about this reaction is true? a) it is an endothermic reaction b) the average kinetic energy of the product remains constant c) it is an exothermic reaction d) the potential energy of the reactants is the same as the potential energy of the product. 5) two samples of gold that have different temperatures are placed in contact with one another. heat will flow spontaneously from a sample of gold at 60°c to a sample of gold that has a temperature of a) 323k b) 333k c) 343k d) 353k 6) a sample of helium gas is in a sealed, rigid container. what occurs as the temperature of the sample is increased? a) the mass of the sample decreases. b) the number of moles of gas increases. c) the volume of each atom decreases. d) the frequency of collisions between atoms increases. 7) given the equation: i₂(s) → i₂(g) which phrase describes this change? a) endothermic chemical change b) endothermic physical change c) exothermic chemical change d) exothermic physical change 8) which sample of matter sublimes at room temperature and standard pressure? a) br₂(l) b) cl₂(g) c) co₂(s) d) so₂(aq) 9) given the reaction: iron combines with sulphur to produce iron sulphide and heat energy. which statement about this reaction is true? a) it is an endothermic reaction b) the average kinetic energy of the product remains constant c) it is an exothermic reaction d) the potential energy of the reactants is the same as the potential energy of the product. 10) as a result of dissolving a salt in water, a student found that the temperature of the water increased. from this observation alone, the student should conclude that the dissolving of the salt a) produced an acid solution b) was endothermic c) produced a basic solution d) was exothermic 11) the average kinetic energy of water molecules decreases when a) h₂o(l) at 337 k changes to h₂o(l) at 300. k b) h₂o(l) at 373 k changes to h₂o(g) at 373 k c) h₂o(s) at 200. k changes to h₂o(s) at 237 k d) h₂o(s) at 273 k changes to h₂o(l) at 273 k 12) a container of salt water was left open for 2 weeks. after that time only the salt was left in the container. explain why the evaporation that occurred during the investigation is an endothermic process.

Explanation:

1. C. phases of matter
2. C. an exothermic reaction
3. (Drawing instruction: Use key to draw at least five CO₂ gas - molecules spread out in the box, representing a gas phase)
4. C. It is an exothermic reaction
5. A. 323K
6. D. The frequency of collisions between atoms increases.
7. B. endothermic physical change
8. C. CO2(s)
9. C. It is an exothermic reaction
10. D. was exothermic
11. A. H₂O(l) at 337 K changes to H₂O(l) at 300. K
12. Evaporation requires heat energy input from the surroundings to change the liquid - water in the salt - water solution to water vapor, so it is an endothermic process.

Answer:

1. C. phases of matter
2. C. an exothermic reaction
3. (Drawing instruction: Use key to draw at least five CO₂ gas - molecules spread out in the box, representing a gas phase)
4. C. It is an exothermic reaction
5. A. 323K
6. D. The frequency of collisions between atoms increases.
7. B. endothermic physical change
8. C. CO2(s)
9. C. It is an exothermic reaction
10. D. was exothermic
11. A. H₂O(l) at 337 K changes to H₂O(l) at 300. K
12. Evaporation requires heat energy input from the surroundings to change the liquid - water in the salt - water solution to water vapor, so it is an endothermic process.