6.1: Endothermic and Exothermic Processes

Open Ended

What is one thing you know about endothermic vs exothermic reactions?

Multiple Choice

Consider the ice being the system. Which is true?

• Heat is being transferred to the surroundings

• Heat is being transferred to the system

Multiple Choice

Consider the liquid water being the soundings. Which is true?

• Heat is being transferred from the surroundings

• Heat is being transferred from the system

Multiple Choice

Consider an egg being cooked. The egg is the system. Which of the following is true?

• This is an endothermic reaction

• This is an exothermic reaction

Multiple Choice

Is this endothermic or exothermic?

• exothermic

• endothermic

Multiple Choice

Is this endothermic or exothermic?

• exothermic

• endothermic

Multiple Choice

In an exothermic reaction, the temperature of products is typically HIGHER than the temperature of the reactants.

• False

• True

Multiple Choice

In an endothermic reaction, the temperature of products is typically HIGHER than the temperature of the reactants.

• False

• True

Multiple Choice

Which one describes an endothermic reaction best?

• reactants + energy --> products

• reactants - energy --> products

• products - energy --> reactants

• products + energy --> reactants

Multiple Choice

Which one describes an exothermic reaction best?

• reactants --> products + energy

• products --> reactants - energy

• products --> reactants + energy

• reactants --> products - energy

Multiple Choice

This graph is an example of what type of reaction?

• Endothermic

• Exothermic

Multiple Choice

This graph is an example of what type of reaction?

• Endothermic

• Exothermic

Potential Quiz Questions

Multiple Choice

The dissolution of an ionic solute in a polar solvent can be imagined as occurring in three steps, as shown in the figure above. In step 1, the separation between the ions in the solute is greatly increased, just as will occur when the solute dissolves in the polar solvent. In step 2, the polar solvent is expanded to make spaces that the ions will occupy In the last step, the ions are inserted into the spaces in the polar solvent. Which of the following best describes the enthalpy change, H for each step?

• All three steps are exothermic

• All three steps are endothermic

• steps 1 and 2 are exothermic, and the final step is endothermic

• Steps 1 and 2 are endothermic and the final step is exothermic

Multiple Choice

For a classroom demonstration, a chemistry teacher puts samples of two different pure solid powders in a beaker. The teacher places the beaker on a small wooden board with a wet surface, then stirs the contents of the beaker. After a short time the students observe that the bottom of the beaker is frozen to the wood surface. The teacher asks the students to make a claim about the observation and to justify their claims. Which of the following is the best claim and justification based on the students' observation?

• An endothermic chemical change occurred because the temperature of the beaker and the water on the board decreased as heat was absorbed by the reaction

• An exothermic physical change occurred because heat flowed from the contents of the beaker and the water on the board to the room

• An endothermic physical change occurred because the freezing of water is an endothermic process

• An exothermic chemical change occurred because heat flowed from the contents of the beaker to the room

Multiple Choice

Which of the following phase changes involves the transfer of heat from the surroundings to the system?

Multiple Choice

In the spring, blossoms on the cherry trees can be damaged when temperatures fall below -2 C. When the forecast calls for air temperatures to be below -5 C for a few hours one night, a farmer sprays his blossoming cherry trees with water, claiming that the blossoms will be protected by the water as it freezes. Which of the following is a correct justification for spraying water on the blossoms?

• Water on the blossoms will not freeze unless the air temperature falls significantly below -5 C

• The freezing of water is an exothermic process; thus water that freezes on the blossoms releases heat to keep the blossoms at or above -2 C

• The freezing of water is an endothermic process; thus, water that freezes on the blossoms absorbs heat from the atmosphere, which in turn keeps the blossoms above 0 C

• Water is a good thermal conductor that transfers heat from the cold air to the blossoms, keeping hte blossoms from going below -2 C