Final answer:
The water and carbon dioxide produced in the reaction between copper oxide and methane are in the gas phase and escape from the test tube because they diffuse into the surrounding atmosphere.
Step-by-step explanation:
The equation provided shows the chemical reaction where copper oxide (CuO) reacts with methane (CH4) to produce copper (Cu), water (H2O), and carbon dioxide (CO2). The water and carbon dioxide produced in this reaction are in the gas phase, as denoted by the (g) after their chemical formulas. Gases tend to escape from an open system, such as a test tube in a laboratory, because they have higher kinetic energy and can diffuse into the surrounding atmosphere. Since the reaction is not in a closed system, these products are not contained, allowing them to escape from the test tube.