📚 Topic Summary
Surface tension is a phenomenon where the surface of a liquid acts like a stretched elastic membrane. This is due to the cohesive forces between liquid molecules. Molecules at the surface experience a net inward pull, creating tension. Stronger intermolecular forces lead to higher surface tension. Temperature also affects surface tension; as temperature increases, surface tension generally decreases.
🧪 Part A: Vocabulary
Match the terms with their definitions:
| Term |
Definition |
| 1. Cohesion |
A. The energy required to increase the surface area of a liquid by a unit amount. |
| 2. Adhesion |
B. The force of attraction between molecules of different substances. |
| 3. Surface Tension |
C. A measure of how difficult it is to stretch or break the surface of a liquid. |
| 4. Capillary Action |
D. The ability of a liquid to flow in narrow spaces without the assistance of external forces like gravity. |
| 5. Surface Energy |
E. The force of attraction between molecules of the same substance. |
Matching Answers: 1-E, 2-B, 3-C, 4-D, 5-A
✍️ Part B: Fill in the Blanks
Complete the following paragraph using the words: intermolecular, decreases, surface tension, cohesive, temperature.
__________ is caused by __________ forces between liquid molecules. As __________ increases, the __________ of a liquid generally __________.
Answer: Surface tension, cohesive, temperature, surface tension, decreases, intermolecular
🤔 Part C: Critical Thinking
Explain how surfactants reduce the surface tension of water and provide a real-world example of their use.
Answer: Surfactants are substances that reduce the surface tension of a liquid by disrupting the intermolecular forces between the liquid molecules. They typically have a hydrophobic (water-repelling) part and a hydrophilic (water-attracting) part. When added to water, the hydrophobic parts of the surfactant molecules orient away from the water, while the hydrophilic parts orient towards the water. This arrangement reduces the net inward pull on the surface molecules, thereby lowering the surface tension. A real-world example is the use of soap. Soap molecules act as surfactants, reducing the surface tension of water and allowing it to spread more easily and wet surfaces, thus aiding in cleaning.