Chemistry Chapter on Enthalpy and Reactions

What does a positive change in enthalpy (ΔH) indicate about a reaction?

In an exothermic reaction, what happens to the temperature of the surroundings?

What does the activation energy represent in a chemical reaction?

Which statement is true regarding an endothermic reaction?

What role does a catalyst play in a chemical reaction?

During a reaction that produces water from hydrogen and oxygen, which statement is correct?

What can be inferred about the products in an endothermic reaction compared to the reactants?

Which of the following is true about the heat of reaction (ΔH) for an exothermic process?

Enthalpy

Enthalpy (H) is the measure of heat energy.
Change in enthalpy (ΔH) reflects energy required or released during a reaction.
ΔH = Hproducts – Hreactants
Positive ΔH means energy is absorbed (endothermic).
Negative ΔH means energy is released (exothermic).

Endothermic Reaction

Heat (energy) is absorbed.
Feels cold and temperature decreases.
Products have more energy than reactants.
ΔH is positive.

Exothermic Reaction

Heat (energy) is released.
Feels hot and temperature increases.
Reactants have more energy than products.
ΔH is negative.

Collision Theory

Atoms, ions, or molecules react to form products when they collide, IF, they have enough energy.
This energy is called Activation Energy.
The minimum energy colliding particles need to have to react.
For example, the reaction between hydrogen and oxygen to form water: 2H2 + O2 🡪 2H2O

Activated Complex

An unstable arrangement of atoms that forms momentarily at the activation-energy barrier.
Also known as the transition state.

Endothermic or Exothermic

The energy of products is higher than reactants in an endothermic reaction.
The Heat of Reaction (ΔH) is positive for endothermic reactions.
The energy of products is lower than reactants in an exothermic reaction.
The Heat of Reaction (ΔH) is negative for exothermic reactions.

Catalyst

A catalyst increases the rate of reaction by lowering the activation-energy barrier.
A catalyst does not affect the Heat of Reaction.

This quiz covers key concepts related to enthalpy, including endothermic and exothermic reactions, as well as collision theory. You'll explore how energy changes during chemical reactions and the role of activation energy. Test your understanding of these fundamental chemistry principles.