5 - Enthalpy SCH4U – Thermochemistry
Date: ______
Enthalpy, ΔH
- The total ______of a substance at a constant pressure
- Chemists study the enthalpy ______, ΔH, that accompanies a chemical process
- Enthalpy is the heat ______or ______during a chemical reaction
- The enthalpy of a reaction results from changes in the ______of the ______
- Calculated by measuring the heat ______in a reaction
Reaction Coordinates
- When dealing with the energy changes of reactions, we can look at a graph of ______versus ______(reaction coordinate)
- Enthalpy changes for exothermic reactions are given a ______sign or written on the product side of the equation with a ______sign
- For exothermic reactions, the products have ______energy than the reactants
- Enthalpy changes for endothermic reactions are given a ______sign or written on the reactant side of the equation with a ______sign
- For endothermic reactions, the products have ______energy than the reactants
Molar Enthalpy
- The enthalpy change associated with one ______
H2(g) + ½ O2(g) → H2O(g) + 242 kJ
- The energy is a product so this reaction is ______
Example:
- What mass of water is formed from hydrogen and oxygen when 831 kJ of heat is produced?
Example:
- Freon-12 (CCl2F2) is a common refrigerant that is vaporized in tubes inside a refrigerator, releasing heat. This results in heat being released to the outside of the fridge. If 500.0 g of the Freon is vaporized, what is the total expected enthalpy change, ΔH? ΔH for Freon-12 is 34.99 .
Example:
- 7.46 g of potassium chloride is dissolved in 100.0 mL of water at an initial temperature of 24.1°C. The final temperature of the solution is 20.°C. What is the molar enthalpy for dissolving the potassium chloride?
Enthalpy is a State Function
- A state function is a function that only depends on the ______states of the reaction
- Does not depend on the ______to get from reactants to products
Homework
Page 308
Questions 1-3
Page 2 of 3