Chapter 9 Flashcards
What is enthalpy H?
a measure of the heat energy in a chemical system
What does the chemical system refer to?
the atoms, molecules, or ions making up the chemicals
Can enthalpy be measured?
no
Can enthalpy changes be measured?
yes
What is the enthalpy change ΔH?
the difference in enthalpies
ΔH =
H(products) - H(reactants)
Is ΔH positive or negative?
it can be either
What does the value of ΔH depend on?
whether the products contain more or less energy than the reactants
What is the law of conservation of energy?
energy cannot be created or destroyed
In a chemical reaction involving an enthalpy change, where is heat energy transferred between?
the system and the surroundings
What is the system?
the chemicals - the reactants and products
What are the surroundings?
the apparatus, the laboratory, and everything that is not the chemical; system
What is the universe?
everything, including the system and surroundings
Can an enthalpy change ΔH be determined experimentally?
yes
How can an enthalpy change ΔH be determined experimentally?
by measuring the energy transfer between the sustem and the surroundings
What two directions can energy transfer be?
1) exothermic - from the system to the surroundings
2) endothermic - from the surroundings to the system