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Given the key:
Which particle model diagram represents a chemical change?*
When a sample of CO2(s) becomes CO2(g), there is a change in*
Which process is a chemical change?*
Which change is most likely to occur when a molecule of H2 and a molecule of I2 collide with proper orientation and sufficient energy?*
Which processes represent one chemical change and one physical change?*
Which change results in the formation of different substances?*
Which statement describes a chemical change?*
Based on Table I, which compound dissolves in water by an exothermic process?*
During which two processes does a substance release energy?*
Base your answers to questions 10 on the information below and on your knowledge of chemistry.
Starting as a solid, a sample of a molecular substance is heated, until the entire sample of the substance is a gas. The graph below represents the relationship between the temperature of the sample and the elapsed time.
State evidence that indicates the sample undergoes only physical changes during this heating.*
Base your answers to questions 11 on the information below and on your knowledge of chemistry.
Wood is mainly cellulose, a polymer produced by plants. One use of wood is as a fuel in campfires, fireplaces, and wood furnaces. The molecules of cellulose are long chains of repeating units. Each unit of the chain can be represented as C6H10O5. The balanced equation below represents a reaction that occurs when C6H10O5 is burned in air.
C6H10O5 + 6O2 → 6CO2 + 5H2O + heat
Explain, in terms of substances in the reaction, why the equation represents a chemical change.*
Base your answers to questions 12 on the information below.
The reaction between aluminum and an aqueous solution of copper(II) sulfate is represented by the unbalanced equation below.
Al(s) + CuSO4(aq) → Al2(SO4)3(aq) + Cu(s)
Explain why the equation represents a chemical change.*
Base your answers to questions 13 on the information below and on your knowledge of chemistry.
In a laboratory activity, each of four different masses of KNO3(s) is placed in a separate test tube that contains 10.0 grams of H2O at 25°C.
When each sample is first placed in the water, the temperature of the mixture decreases. The mixture in each test tube is then stirred while it is heated in a hot water bath until all of the KNO3(s) is dissolved. The contents of each test tube are then cooled to the temperature at which KNO3 crystals first reappear. The procedure is repeated until the recrystallization temperatures for each mixture are consistent, as shown in the table below.
Based on Table I, explain why there is a decrease in temperature when the KNO3(s) was first dissolved in the water.*
Base your answers to questions 14 on the information below and on your knowledge of chemistry.
Nitrogen dioxide, NO2, is a dark brown gas that is used to make nitric acid and to bleach flour. Nitrogen dioxide has a boiling point of 294 K at 101.3 kPa. In a rigid cylinder with a movable piston, nitrogen dioxide can be in equilibrium with colorless dinitrogen tetroxide, N2O4. This equilibrium is represented by the equation below.
2NO2(g) ⇌ N2O4(g) + 58 kJ
State evidence from the equation that the forward reaction is exothermic.*
Base your answers to questions 15 on the information below and on your knowledge of chemistry.
During photosynthesis, plants use carbon dioxide, water, and light energy to produce glucose, C6H12O6, and oxygen. The reaction for photosynthesis is represented by the balanced equation below.
6CO2 + 6H2O + light energy → C6H12O6 + 6O2
State evidence that indicates photosynthesis is an endothermic reaction.*