How do I know which enthelpy change to calculate?

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In summary, the difference between finding the enthalpy of combustion and the enthalpy of formation depends on the question being asked. The standard enthalpy change of combustion is the energy released when one mole of a compound is burned completely in oxygen under standard conditions, while the standard enthalpy change of formation is the energy required to form one mole of a compound from its constituent elements in their standard states.
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How do I know if I need to find the enthalpy of combustion or the enthalpy of formation? I know the equation to find the enthalpy change of each them but I don't know on a question if I have to find the enthalpy of combustion or the enthalpy of formation.
 
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It must depend on the question, there is no "one size fits all" answer.
 
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The standard enthalpy change of combustion of a compound is the enthalpy change which occurs when one mole of the compound is burned completely in oxygen under standard conditions, and with everything in its standard state.

https://www.chemguide.co.uk/physical/energetics/definitions.html
 

1. What is enthalpy and why is it important in scientific calculations?

Enthalpy is a thermodynamic quantity that measures the total energy of a thermodynamic system. It is important in scientific calculations because it helps us understand and predict how energy is transferred and transformed in a system.

2. How do I determine which enthalpy change to calculate?

The enthalpy change to calculate depends on the specific system or process you are studying. It could be a change in enthalpy during a chemical reaction, a phase change, or a change in temperature. It is important to clearly define the system and process in order to determine the appropriate enthalpy change to calculate.

3. What is the difference between enthalpy of reaction and enthalpy of formation?

The enthalpy of reaction is the change in enthalpy that occurs during a chemical reaction, while the enthalpy of formation is the change in enthalpy that occurs when one mole of a compound is formed from its constituent elements in their standard states. In other words, the enthalpy of formation is specific to a particular compound, while the enthalpy of reaction can vary depending on the specific reaction.

4. How do I calculate the enthalpy change for a chemical reaction?

To calculate the enthalpy change for a chemical reaction, you will need to know the enthalpy of formation for each reactant and product involved in the reaction. Then, you can use the formula ΔH = ΣnΔHf(products) - ΣnΔHf(reactants), where n is the number of moles of each substance.

5. Can enthalpy changes be negative?

Yes, enthalpy changes can be negative. A negative enthalpy change indicates that energy is being released from the system, while a positive enthalpy change indicates that energy is being absorbed by the system. This can occur during exothermic and endothermic reactions, respectively.

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