The overall enthalpy change for a reaction is the sum of the enthalpy changes for each individual step.
True
What is enthalpy change (ΔH) in a chemical reaction?
Heat energy released or absorbed
The overall enthalpy change for a reaction is the same whether it occurs in one step or multiple steps.
True
Hess's Law states that the overall enthalpy change for a chemical reaction is the same whether it occurs in one step or multiple steps
What is the fundamental principle of Hess's Law regarding the overall enthalpy change of a reaction?
Independent of reaction pathway
What is the key concept of Hess's Law regarding the enthalpy change of a reaction?
Overall ΔH is pathway-independent
Exothermic reactions have a negative ΔH and release heat to the surroundings.
True
Steps to calculate enthalpy change using Hess's Law:
1️⃣ Identify the target reaction
2️⃣ Arrange known reactions
3️⃣ Adjust reactions if needed
4️⃣ Sum adjusted enthalpy changes
Steps to apply Hess's Law to calculate the enthalpy change of a target reaction.
1️⃣ Identify the target reaction
2️⃣ Arrange known reactions
3️⃣ Adjust reactions if needed
4️⃣ Sum adjusted enthalpy changes
Match the action with its explanation in Hess's Law.
Identify the target reaction ↔️ Clearly state the reaction whose ΔH needs to be calculated
Adjust reactions if needed ↔️ Reverse or multiply reactions to match the target, adjusting ΔH
Sum adjusted enthalpy changes ↔️ Add the ΔH values of each step to find the overall ΔH
Multiplying equation 1 (C(s) + ½ O₂(g) → CO(g)) by 2 results in a new ΔH'₁ value of -221.0 kJ/mol.
Hess's Law can be used to calculate the enthalpy of formation of a compound.
True
Match the reaction step with its enthalpy change:
Step 1 ↔️ ΔH₁
Step 2 ↔️ ΔH₂
Step 3 ↔️ ΔH₃
Overall ↔️ ΔH₁ + ΔH₂ + ΔH₃
Order the steps to calculate the overall enthalpy change using Hess's Law:
1️⃣ Identify the target reaction
2️⃣ Break the target reaction into steps
3️⃣ Determine the enthalpy change for each step
4️⃣ Sum the enthalpy changes
What is the fundamental principle of Hess's Law?
Overall ΔH is constant
What does the enthalpy change (ΔH) measure in a chemical reaction?
Heat energy released or absorbed
The total ΔH for a reaction is the sum of the enthalpy changes for each individual step, regardless of the reaction pathway.
True
Hess's Law states that the enthalpy change for a chemical reaction is the same whether the reaction occurs in one step or in multiple steps
For the formation of CO₂(g) from C(s) and O₂(g), the overall enthalpy change is -393.5 kJ/mol
What is the enthalpy change for the decomposition of calcium carbonate (CaCO₃)?
+178 kJ/mol
To calculate the ΔH for CO₂(g) → CO(g) + ½ O₂(g), you must reverse reaction 2, resulting in a ΔH'₂ value of +283.0 kJ/mol.
What is the new enthalpy change (ΔH'₂) for the reversed reaction CO₂(g) → CO(g) + ½ O₂(g)?
+283.0 kJ/mol
Reversing a reaction in Hess's Law requires changing the sign of its enthalpy change.
True
Steps to calculate the enthalpy change for the reaction 2CO(g) + O₂(g) → 2CO₂(g) using Hess's Law.
1️⃣ Multiply equation 1 by 2
2️⃣ Multiply equation 2 by 2
3️⃣ Reverse equation 1
4️⃣ Combine equations
What is one common application of Hess's Law in AP Chemistry?
Combustion enthalpy calculations
Hess's Law states that the enthalpy change for a chemical reaction is the same whether the reaction occurs in one step or in multiple steps
The overall enthalpy change in a reaction is independent of the reaction pathway.
True
Hess's Law states that the sum of enthalpy changes for each step equals the total enthalpy change of the reaction
What does it mean for enthalpy change to be independent of the pathway in Hess's Law?
Total ΔH remains constant
Hess's Law states that the overall enthalpy change (ΔH) for a reaction is the same, whether the reaction occurs in one step or in multiple steps
Match the step with its corresponding enthalpy change:
Step 1 ↔️ ΔH₁
Step 2 ↔️ ΔH₂
Step 3 ↔️ ΔH₃
Overall ΔH ↔️ ΔH₁ + ΔH₂ + ΔH₃
If a reaction can be broken into steps with known enthalpy changes, their sum equals the overall enthalpy change.
True
Match the reaction type with its enthalpy change and heat release/absorption:
Exothermic ↔️ Negative ΔH, heat released
Endothermic ↔️ Positive ΔH, heat absorbed
To calculate the enthalpy change of a target reaction using Hess's Law, the first step is to identify the target reaction
Hess's Law states that the enthalpy change of a reaction is independent of the path taken to reach the final state.
True
When reaction 1 (C(s) + ½ O₂(g) → CO(g)) and the reversed reaction 2 are combined, the final ΔH for the reaction C(s) + O₂(g) → CO₂(g) is +172.5 kJ/mol.
What is the overall ΔH for the reaction CO₂(g) → C(s) + O₂(g) using the given enthalpy changes?
+172.5 kJ/mol
What is the final ΔH for the reaction 2CO(g) + O₂(g) → 2CO₂(g) using Hess's Law?