Enthalpy and Energy Changes in Reactions

This lesson introduces energy changes in chemical reactions, focusing on enthalpy, exothermic, and endothermic reactions. It explains how energy is released or absorbed during chemical bonding and provides examples of both reaction types. Practical demonstrations illustrate these concepts, and the lesson concludes with a summary and next steps for further learning.

What happens to energy when two atoms form a bond?

• Energy is destroyed.

• Energy remains constant.

• Energy is released.

• Energy is absorbed.

How is enthalpy change (ΔH) calculated in a chemical reaction?

• Final enthalpy minus initial enthalpy

• Initial enthalpy minus final enthalpy

• Reactant enthalpy minus product enthalpy

• Product enthalpy plus reactant enthalpy

Which of the following is an example of an exothermic reaction?

• Electrolysis of water

• Melting ice

• Evaporating water

• Burning a candle

In an endothermic reaction, how does the energy of the products compare to the reactants?

• Energy is not involved.

• Products have less energy than reactants.

• Products have more energy than reactants.

• Products have the same energy as reactants.

Which process is an example of an endothermic reaction?

• Neutralization of acids and bases

• Melting of ice

• Crystallization of salt

• Combustion of fossil fuels

What chemical is used in cold packs to create an endothermic reaction?

• Calcium chloride

• Ammonium nitrate

• Sodium sulfate

• Magnesium oxide

What happens when calcium chloride is mixed with water in a hot pack?

• The solution remains unchanged.

• The solution becomes hot.

• The solution evaporates.

• The solution becomes cold.

What is the role of ammonium nitrate in an instant cold pack?

• It releases heat.

• It absorbs heat.

• It remains inert.

• It evaporates.

What is the main characteristic of an exothermic reaction?

• Energy is absorbed from the surroundings.

• Energy is released to the surroundings.

• Energy remains constant.

• Energy is converted to mass.

What is the significance of enthalpy in chemical reactions?

• It shows the speed of the reaction.

• It represents the heat energy change at constant pressure.

• It indicates the color change in reactions.

• It measures the mass of reactants.