why can't the enthalpy of magnesium be measured using a coffee cup calorimeter?
I assume you mean Mg to MgO. How will you burn Mg under water?
No, the question only says Mg
Then I have no idea what the question means. The delta Hformation Mg is zero. For anything else with Mg there must be some kind of reaction.
The enthalpy of magnesium cannot be directly measured using a coffee cup calorimeter because the reaction of magnesium with oxygen is highly exothermic and can cause an extremely rapid and violent reaction. Since the reaction releases a large amount of heat, it can potentially melt through the walls of a coffee cup calorimeter, leading to safety hazards and inaccurate measurements.
To measure the enthalpy of magnesium oxidation, an alternative method, such as bomb calorimetry or a specialized reaction vessel, is typically used. These methods are designed to handle high-energy reactions safely and accurately.
It's also important to note that measuring the enthalpy change of a reaction involves taking into account the heat exchange between the system (substances undergoing the chemical reaction) and the surroundings (calorimeter and its contents). A coffee cup calorimeter is not well-suited for accurately measuring the enthalpy change of highly exothermic reactions like magnesium oxidation due to the limitations in containment and heat transfer.