HeSs law

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What is Hess's Law?

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Hess's Law states that the total enthalpy change for a reaction is the same, regardless of the number of steps the reaction takes. It allows for the calculation of enthalpy changes in complex reactions by summing the enthalpy changes of individual steps.

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Define endothermic reaction.

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An endothermic reaction is a chemical reaction that absorbs energy from its surroundings, usually in the form of heat, resulting in a temperature decrease in the surroundings.

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Define exothermic reaction.

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An exothermic reaction is a chemical reaction that releases energy to its surroundings, usually in the form of heat, resulting in a temperature increase in the surroundings.

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What is the enthalpy change (ΔH) for an endothermic reaction?

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The enthalpy change (ΔH) for an endothermic reaction is positive, indicating that energy is absorbed.

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What is the enthalpy change (ΔH) for an exothermic reaction?

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The enthalpy change (ΔH) for an exothermic reaction is negative, indicating that energy is released.

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How do you determine if a reaction is endothermic or exothermic based on temperature change?

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If the temperature of the surroundings decreases, the reaction is endothermic. If the temperature of the surroundings increases, the reaction is exothermic.

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What is the standard enthalpy of formation (ΔHf°)?

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The standard enthalpy of formation (ΔHf°) is the change in enthalpy when one mole of a compound is formed from its elements in their standard states.

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How is Hess's Law applied in calculating enthalpy changes?

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Hess's Law is applied by breaking down a reaction into multiple steps, calculating the enthalpy change for each step, and then summing these changes to find the total enthalpy change for the overall reaction.

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What is the significance of a negative enthalpy change in a reaction?

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A negative enthalpy change indicates that the reaction is exothermic, meaning it releases energy to the surroundings.

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What is the significance of a positive enthalpy change in a reaction?

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A positive enthalpy change indicates that the reaction is endothermic, meaning it absorbs energy from the surroundings.