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Which statement describes a chemical change?*
Which processes represent one chemical change and one physical change?*
Which process is a chemical change?*
Given the key:
Which particle model diagram represents a chemical change?*
Which change results in the formation of different substances?*
Which change is most likely to occur when a molecule of H2 and a molecule of I2 collide with proper orientation and sufficient energy?*
When a sample of CO2(s) becomes CO2(g), there is a change in*
Base your answers to questions 9 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 10 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 11 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 12 on the information below.
Ammonium chloride is dissolved in water to form a 0.10 M NH4Cl(aq) solution. This dissolving process is represented by the equation below.
State evidence that indicates the dissolving of ammonium chloride is an endothermic process.*
Base your answers to questions 13 on the information below and on your knowledge of chemistry.
Seawater contains dissolved salts in the form of ions. Some of the ions found in seawater are Ca2+, Mg2+, K+, Na+, Cl−, HCO3−, and SO42−. An investigation was conducted to determine the concentration of dissolved salts in seawater at one location. A 300.-gram sample of the seawater was placed in an open container. After a week, all the water had evaporated and 10. grams of solid salts remained in the container.
Explain why the evaporation that occurred during the investigation is an endothermic process.*
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.
At standard pressure, hydrogen peroxide, H2O2, melts at −0.4°C, boils at 151°C, and is very soluble in water. A bottle of aqueous hydrogen peroxide, H2O2(aq), purchased from a pharmacy has a pressure-releasing cap. Aqueous hydrogen peroxide decomposes at room temperature, as represented by the balanced equation below.
2H2O2(aq) → 2H2O(ℓ) + O2(g) + 196.0 kJ
State evidence that indicates the decomposition of H2O2(aq) is exothermic.*
