R1.2 Energy Cyles in Reactions Flashcards
(41 cards)
What is bond enthalpy?
The amount of energy required to break one mole of a specific type of bond in a gaseous molecule.
True or False: Bond enthalpy is always a positive value.
True
Fill in the blank: The bond enthalpy of a bond is typically measured in _______.
kJ/mol
Which of the following bonds has the highest bond enthalpy? A) C-H B) O-H C) N-H D) F-F
A) C-H
What factors can affect bond enthalpy?
Atomic size, bond order, and the presence of electronegative atoms.
Short Answer: How does bond order relate to bond enthalpy?
Higher bond order generally leads to higher bond enthalpy.
True or False: Double bonds have higher bond enthalpy than single bonds.
True
What is the bond enthalpy of a C=O double bond approximately?
Approximately 799 kJ/mol.
Fill in the blank: The bond enthalpy can be used to estimate the _______ of a chemical reaction.
enthalpy change
Multiple Choice: Which of the following statements is true about bond enthalpy? A) It varies in different states of matter. B) It is the same for all molecules. C) It is specific to the type of bond in a molecule. D) None of the above.
C) It is specific to the type of bond in a molecule.
What is Hess’s Law?
Hess’s Law states that the total enthalpy change during a chemical reaction is the same, regardless of the number of steps in the reaction.
True or False: Hess’s Law applies only to reactions that occur in a single step.
False
Fill in the blank: Hess’s Law is based on the principle of ________, which states that energy cannot be created or destroyed.
conservation of energy
If a reaction can be expressed as the sum of two or more other reactions, what can be said about the enthalpy change of the overall reaction?
It is equal to the sum of the enthalpy changes of the individual reactions.
What is the formula for calculating the enthalpy change using Hess’s Law?
ΔH = ΣΔH(products) - ΣΔH(reactants)
Multiple Choice: Which of the following is an application of Hess’s Law? A) Calculating the speed of a reaction B) Determining the heat of formation C) Measuring pressure changes D) Observing color changes
B) Determining the heat of formation
True or False: Hess’s Law can be used to find the enthalpy change for reactions that are difficult to measure directly.
True
What is the significance of standard enthalpy of formation in relation to Hess’s Law?
It allows for the calculation of enthalpy changes for reactions using standard enthalpy values.
In a reaction where A converts to C via B, if the enthalpy change for A to B is -100 kJ and for B to C is -50 kJ, what is the enthalpy change for A to C?
-150 kJ
What type of thermodynamic quantity is enthalpy?
Enthalpy is a state function.
What is the definition of standard enthalpy change of formation?
It is the change in enthalpy when one mole of a compound is formed from its elements in their standard states.
True or False: The standard enthalpy change of formation for a pure element in its standard state is zero.
True
What symbol is commonly used to represent standard enthalpy change of formation?
ΔH°f
