# Chemical Trends in Experimental Data
Many ACT Science questions ask you to identify trends and relationships in data. This guide covers common patterns in chemistry experiments and how to recognize them quickly.
1. Types of Relationships
Direct (Positive) Relationship
As X increases, Y increases. Example: higher temperature → faster reaction rate.
Inverse (Negative) Relationship
As X increases, Y decreases. Example: higher concentration of acid → lower pH.
No Relationship
Changing X has no effect on Y. Example: catalyst amount doesn't affect final product quantity.
Non-linear Relationships
- Exponential growth/decay
- Plateau (levels off) — e.g. enzyme saturation
- Step changes — e.g. phase transitions
2. Common Chemistry Trends on ACT
| Factor | Effect on Rate | Relationship |
|---|---|---|
| Temperature ↑ | Rate ↑ | Direct |
| Concentration ↑ | Rate ↑ | Direct |
| Particle size ↓ | Rate ↑ | Inverse |
| Catalyst added | Rate ↑ | Faster but same endpoint |
| Factor | Effect on Solubility |
|---|---|
| Temperature ↑ (most solids) | Solubility ↑ |
| Temperature ↑ (gases) | Solubility ↓ |
| Pressure ↑ (gases) | Solubility ↑ |
3. Describing Trends on the ACT
Use precise language:
- "As temperature increases from 20°C to 60°C, the reaction time decreases from 120 s to 15 s"
- "There is an inverse relationship between..."
- "The rate plateaus above 50°C"
4. Practice Questions
- From a graph, describe the relationship between pressure and gas volume.
- Identify which variable has the greatest effect on reaction rate from a table.
- Predict the solubility of a salt at 80°C using a solubility curve.
- Two catalysts are tested. Which produces more product? Which is faster?
- Explain why two experiments produce the same final amount of product at different rates.
Want to check your answers and get step-by-step solutions?
5. ACT Tips
- Look for the OVERALL trend, not individual data points
- If a graph curves, note where it's steepest (fastest change)
- Use specific values from the data to support trend descriptions
- Don't assume causation from correlation alone
- Trends may reverse at certain points — note these turning points