Question

a piece of dry ice (solid co₂) was placed inside a balloon and the balloon was tied and sealed so that no carbon dioxide escapes. the initial mass of the balloon and the dry ice was 20.00 g. the dry ice was allowed to sublime into a gas and then the balloon was weighed again. what do you expect the balloon to weigh once the dry ice has sublimed to form gas?
oa the balloon will be less than 20.00 g, because as a solid weighs more than a gas.
ob the balloon will be 20.00 g, because the solid has changed to a gas but has not escaped the balloon.
oc the balloon will weigh less than 20.00 g, because the cold will cause the molecules to slow down and shrink the balloon.
od the balloon will weigh more than 20.00 g, because as the dry ice sublimes and forms a gas, the balloon expands making it bigger and weigh more.

Explanation:

According to the law of conservation of mass, mass is neither created nor destroyed in a chemical reaction (in this case, sublimation of dry - ice which is a physical change but mass conservation still applies). The dry - ice (solid \(CO_2\)) sublimates to form gaseous \(CO_2\). Since the balloon is tied and sealed, no \(CO_2\) escapes. So the mass of the balloon should remain the same.

Option A is incorrect because a solid and its corresponding gas (for the same substance) have the same mass per unit amount (molar mass). Option C is incorrect as the cold does not cause a mass change (mass is independent of temperature for a closed system). Option D is incorrect because expansion due to gas formation does not add mass. Option B is correct as the mass of the solid \(CO_2\) is equal to the mass of the gaseous \(CO_2\) formed (no escape) and the balloon will weigh \(20.00\) g.

Answer:

B. The balloon will be \(20.00\) g, because the solid has changed to a gas but has not escaped the balloon.