This resource focuses on the concept of phase changes, specifically how heat energy causes a solid to transition into a liquid. Through the scenario of a chocolate bar melting in a warm backpack, students are guided to construct a Claim-Evidence-Reasoning (CER) explanation. They will reflect on their observations from class experiments with ice and wax, using structured sentence stems to articulate their claims about the state change. The exercise includes a checklist for self-assessment of their explanations, along with a challenge question about reversing the melting process and a metacognitive calibration to assess their confidence in understanding and explaining these scientific concepts.