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Questions and Answers
What is the enthalpy change for an exothermic reaction?
What is the enthalpy change for an exothermic reaction?
- Positive
- Negative (correct)
- Zero
- It could be positive or negative
Which process is an example of an endothermic reaction?
Which process is an example of an endothermic reaction?
- Boiling of water
- Melting of ice (correct)
- Combustion of propane
- Nuclear fission of U-235
During nuclear fission, what is absorbed that initiates the process?
During nuclear fission, what is absorbed that initiates the process?
- Neutron (correct)
- Heat
- Photon
- Oxygen
In an endothermic reaction, how does the enthalpy of reactants compare to the enthalpy of products?
In an endothermic reaction, how does the enthalpy of reactants compare to the enthalpy of products?
Which of the following is true for combustion reactions involving hydrocarbons?
Which of the following is true for combustion reactions involving hydrocarbons?
Which statement is true about the enthalpy of reaction for an endothermic process?
Which statement is true about the enthalpy of reaction for an endothermic process?
What is a common characteristic of exothermic reactions?
What is a common characteristic of exothermic reactions?
What occurs during an endothermic reaction?
What occurs during an endothermic reaction?
During which reaction is enthalpy usually represented as a negative value?
During which reaction is enthalpy usually represented as a negative value?
What does the prefix 'endo' in endothermic imply?
What does the prefix 'endo' in endothermic imply?
Which part of a chemical reaction typically requires heat input?
Which part of a chemical reaction typically requires heat input?
How can you describe the enthalpy of a system?
How can you describe the enthalpy of a system?
Why does a glass of lemonade become colder when ice cubes melt?
Why does a glass of lemonade become colder when ice cubes melt?
What is the relationship between internal energy and enthalpy of a system?
What is the relationship between internal energy and enthalpy of a system?
In the context of chemical reactions, what does the enthalpy of reaction refer to?
In the context of chemical reactions, what does the enthalpy of reaction refer to?
Flashcards
Endothermic Reaction
Endothermic Reaction
A reaction that absorbs heat from the surroundings.
Exothermic Reaction
Exothermic Reaction
A reaction that releases heat into the surroundings.
Enthalpy
Enthalpy
The heat content of a system, measured in Joules or kilo-Joules.
Enthalpy of Reaction
Enthalpy of Reaction
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Breaking Bonds
Breaking Bonds
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Forming Bonds
Forming Bonds
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Heat Absorption
Heat Absorption
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Heat Release
Heat Release
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Characteristics of Endothermic
Characteristics of Endothermic
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Characteristics of Exothermic
Characteristics of Exothermic
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Melting of Ice
Melting of Ice
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Combustion
Combustion
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Study Notes
Endothermic and Exothermic Reactions
- Reactions are categorized as endothermic or exothermic based on heat transfer.
- Endothermic reactions absorb heat from surroundings.
- Exothermic reactions release heat into surroundings.
- Examples:
- Melting ice is endothermic (absorbs heat).
- Combustion (burning) is exothermic (releases heat).
Defining Endothermic and Exothermic Reactions
- "Endo" means "inside," "exo" means "outside," and "thermic" refers to heat.
- Endothermic reactions absorb heat.
- Exothermic reactions release heat.
Enthalpy and Reactions
- Enthalpy (H) measures a system's heat content (energy).
- Measured in Joules (J) or Kilojoules (kJ).
- Enthalpy of reaction (ΔH) is the difference between product and reactant enthalpies.
- Breaking bonds absorbs energy (endothermic); forming bonds releases energy (exothermic).
- ΔH = ΣEnthalpy of reactants - ΣEnthalpy for products
Identifying Endothermic and Exothermic Reactions
- Endothermic: ΔH is positive; heat is absorbed.
- Exothermic: ΔH is negative; heat is released.
Endothermic vs Exothermic Summary
| Feature | Endothermic Reactions | Exothermic Reactions |
|---|---|---|
| Heat Transfer | Absorbs heat | Releases heat |
| Enthalpy of reactants vs products | Reactants > Products | Products > Reactants |
| ΔH | Positive | Negative |
Endothermic and Exothermic Examples
- Melting ice: Endothermic; ice absorbs heat to melt.
- Photosynthesis: Endothermic; plants absorb sunlight energy to produce food.
- Combustion: Exothermic; reactions with oxygen release heat (e.g., burning propane).
- Nuclear fission: Exothermic; splitting heavy atoms releases substantial energy.
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