ΔH represents the change in enthalpy, specifically the difference between the enthalpy of products and reactants for a reaction. It indicates whether heat is released (-ΔH) or absorbed (+ΔH).
Think of ΔH as an "energy scorecard" that keeps track of how much energy is gained or lost during a reaction, similar to how a scoreboard tracks points in a game.
Exothermic Reaction: A chemical reaction where heat is released to the surroundings. (-ΔH)
Endothermic Reaction: A chemical reaction where heat is absorbed from the surroundings. (+ΔH)
Thermochemistry: The branch of chemistry that studies the relationship between heat and chemical reactions.
Negative ΔH could mean that...
The combustion of methane (CH₄) has a ΔH value of -890 kJ/mol. What is the ΔH for the reaction: 2CH₄(g) → C₂H₂(g) + 3H₂(g)?
The reaction between sodium (Na) and chlorine (Cl₂) has a ΔH value of -411 kJ/mol. What is the ΔH for the reaction: NaCl(s) → Na(s) + 1/2Cl₂(g)?
The reaction between nitrogen (N₂) and oxygen (O₂) to form nitrogen monoxide (NO) has a ΔH value of 90.3 kJ/mol. What is the ΔH for the reaction: 2NO(g) → N₂(g) + O₂(g)?
The reaction between hydrogen gas (H₂) and chlorine gas (Cl₂) to form hydrogen chloride (HCl) has a ΔH value of -92.3 kJ/mol. What is the ΔH for the reaction: 2HCl(g) → H₂(g) + Cl₂(g)?
The reaction between carbon monoxide (CO) and oxygen gas (O₂) to form carbon dioxide (CO₂) has a ΔH value of -283.0 kJ/mol. What is the ΔH for the reaction: 2CO(g) + O₂(g) → 2CO₂(g)?
How much heat (in kJ) is released when 2.00 mol of NaOH is formed in the reaction 2Na₂O₂ (s) + 2H₂O (l) -> 4NaOH (s) + O₂ (g)? ΔH for the reaction is -126 kJ.
Which of the following is not a way to directly find ΔH?
Do you have to manipulate ΔH if you flip a reaction?
Positive ΔH could mean that...
What is the enthalpy change for the reaction: C2H2(g) + 5/2O2(g) → 2CO2(g) + H2O(g) given the following chemical equations: (1) C2H2(g) + 5/2O2(g) → 2CO(g) + H2O(g) ΔH = -636.1 kJ/mol; (2) CO(g) + 1/2O2(g) → CO2(g) ΔH = -283.0 kJ/mol; (3) C2H2(g) + 5/2O2(g) → 2CO2(g) + H2O(g) ΔH = -1299.5 kJ/mol?
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