5.1 - Measuring Energy Changes

• Endothermic Reaction

  A chemical reaction that absorbs energy from the surroundings, usually in the form of heat, resulting in a decrease in temperature. The enthalpy change (ΔH) for an endothermic reaction is positive.
• Exothermic Reaction

  A chemical reaction that releases energy to the surroundings, usually in the form of heat, resulting in an increase in temperature. The enthalpy change (ΔH) for an exothermic reaction is negative.
• Standard Enthalpy Change of Reaction ($\Delta H^\circ_{\text{r}}$​)


  The enthalpy change that occurs when a reaction takes place under standard conditions (100 kPa, 298 K) and in its standard state.
• Standard Enthalpy Change of Formation ($\Delta H^\circ_{\text{f}}$​)


  The enthalpy change when one mole of a compound is formed from its elements in their standard states under standard conditions.
• Standard Enthalpy Change of Combustion ($\Delta H^\circ_{\text{c}}$​)


  The enthalpy change when one mole of a substance is completely burned in oxygen under standard conditions.
• Specific Heat Capacity (c)

  The amount of heat energy required to raise the temperature of one gram of a substance by one degree Celsius. It's used in calculations involving heat transfer in physical and chemical processes.