Endothermic and Exothermic Reactions

During a campfire, which of the following is true about the reaction occurring in the burning wood?

• Energy is absorbed from the surroundings

• Energy is released to the surroundings

• Energy remains constant

• Energy is converted to mass

Answer explanation

The burning wood undergoes a combustion reaction, releasing energy in the form of heat and light to the surroundings. Therefore, the correct choice is that energy is released to the surroundings.

Matilda is conducting an experiment in her science class. She notices that when she mixes two chemicals, the container feels colder. Which of the following best describes the energy change in this endothermic reaction?

• Energy is absorbed and stored

• Energy is released and stored

• Energy is released and not stored

• Energy is absorbed and not stored

Answer explanation

In an endothermic reaction, energy is absorbed from the surroundings, causing the container to feel colder. This absorbed energy is stored in the chemical bonds of the products, making "Energy is absorbed and stored" the correct choice.

During a science experiment, Arjun mixes two chemicals in a beaker and notices that the beaker becomes warm to the touch. Which of the following is a characteristic of this exothermic reaction?

• Temperature of the surroundings decreases

• Temperature of the surroundings increases

• Temperature of the surroundings remains constant

• Temperature of the system decreases

Answer explanation

In an exothermic reaction, energy is released, causing the temperature of the surroundings to increase. Since Arjun's beaker became warm, it indicates that the temperature of the surroundings increases.

In a science experiment, Emily observes a chemical reaction where the temperature of the surroundings decreases. What is the role of reactants in this endothermic reaction?

• Reactants absorb energy

• Reactants release energy

• Reactants remain unchanged

• Reactants convert to products without energy change

Answer explanation

In an endothermic reaction, reactants absorb energy from the surroundings, leading to a decrease in temperature. This energy absorption is essential for the reaction to proceed, making 'Reactants absorb energy' the correct choice.

Elsie and Kiara are conducting an experiment where they mix two chemicals in a beaker. They notice that the beaker feels warmer to the touch. In this exothermic reaction, what happens to the temperature of the surroundings?

• It decreases

• It remains the same

• It increases

• It fluctuates

Answer explanation

In an exothermic reaction, heat is released into the surroundings, causing the temperature of the surroundings to increase. Therefore, the correct answer is that the temperature increases.

During a science experiment, Daniel added solid ammonium chloride to a beaker of water. What happens to the temperature of the liquid?

• The temperature increases

• The temperature decreases

• The temperature remains the same

• The temperature fluctuates

Answer explanation

When solid ammonium chloride dissolves in water, it absorbs heat from the surroundings, leading to a decrease in the temperature of the liquid. Therefore, the correct answer is that the temperature decreases.

Aarav is conducting an experiment in his science class. He wants to demonstrate an exothermic reaction. Which of the following should he choose?

• Melting ice

• Burning wood

• Dissolving ammonium chloride in water

• Photosynthesis

Answer explanation

Burning wood is an exothermic reaction as it releases heat and light energy. In contrast, melting ice and dissolving ammonium chloride absorb heat, while photosynthesis is an endothermic process that requires energy.

Ava is conducting an experiment in her science class. She wants to know which of the following processes absorbs energy from the surroundings. Which process should she choose?

• Freezing water

• Condensing steam

• Photosynthesis

• Combustion

Answer explanation

Photosynthesis is the process by which plants absorb energy from sunlight to convert carbon dioxide and water into glucose and oxygen, making it the correct choice for a process that absorbs energy from the surroundings.

Leo and Anaya are observing a campfire. In this exothermic reaction, how does the energy of the ashes (products) compare to the wood (reactants)?

• Higher than the reactants

• Lower than the reactants

• Equal to the reactants

• Unrelated to the reactants

Answer explanation

In an exothermic reaction like burning wood, energy is released. The energy of the ashes (products) is lower than that of the wood (reactants) because some energy is transformed into heat and light during the reaction.

During a campfire, what is the role of energy in the burning of wood?

• Energy is converted to mass

• Energy remains constant

• Energy is released to the surroundings

• Energy is absorbed from the surroundings

Answer explanation

During the burning of wood, chemical energy stored in the wood is released as heat and light to the surroundings, making 'Energy is released to the surroundings' the correct choice.