Question

lesson 24: systems and energy
which of the following is true about the energy diagram below?
energy diagram with before reaction (system and surroundings) and after reaction (system and surroundings) bars
options:

• the reaction is endothermic
• the system becomes warmer
• the surroundings become warmer
• the reaction is exothermic

Explanation:

• In an endothermic reaction, the system absorbs energy from the surroundings. Looking at the energy diagram, the system's energy increases (the system part of the diagram is taller after the reaction), which means it has absorbed energy. So the reaction is endothermic.
• Since the system absorbed energy (endothermic), the surroundings lose energy. When the surroundings lose energy, they become cooler, not warmer.
• An exothermic reaction is when the system releases energy to the surroundings (system energy decreases, surroundings energy increases). But here the system energy increases, so it's not exothermic.
• If the system absorbed energy (endothermic), its temperature (related to internal energy) would increase if it's a simple case (assuming no phase - change complications for simplicity), so the system becomes warmer.

Answer:

the reaction is endothermic, the system becomes warmer