Which of the following reactions has a positive ΔH and a positive ΔS?

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Q: Which of the following reactions has a positive ΔH and a positive ΔS?

Solution: Sublimation of dry ice (solid CO2 to gas) has a positive ΔH (endothermic) and a positive ΔS (increase in disorder).

Steps: 8

Step 1: Understand what ΔH means. ΔH is the change in enthalpy, which tells us if a reaction absorbs or releases heat.
Step 2: Know that a positive ΔH means the reaction is endothermic, meaning it absorbs heat.
Step 3: Understand what ΔS means. ΔS is the change in entropy, which tells us about the disorder or randomness of a system.
Step 4: Know that a positive ΔS means there is an increase in disorder or randomness in the system.
Step 5: Identify the reaction in question: sublimation of dry ice (solid CO2 to gas).
Step 6: Recognize that when dry ice sublimates, it absorbs heat from the surroundings (positive ΔH).
Step 7: Realize that the transition from solid to gas increases disorder (positive ΔS).
Step 8: Conclude that sublimation of dry ice has both a positive ΔH and a positive ΔS.