Physics and Chemistry: Conservation, Measurement, and Energy Laws

*2. State the law of conservation of energy.*

The law of conservation of energy states that energy cannot be created or destroyed; it can only be transformed from one form to another. This means the total amount of energy in a closed system stays the same over time.

*3. What is the difference between heat and temperature?*

Heat is the total energy transferred between substances due to a temperature difference. Temperature is a measure of how fast the particles in a substance are moving. Heat depends on mass and energy, while temperature is just about particle motion.

*4. What is the difference between a theory and a law?*

A law describes what happens, often with a formula (e.g., gravity). A theory explains why or how something happens. Laws are usually proven and universal; theories are supported by evidence but can evolve.

*5. What is accuracy? What is precision?*

Accuracy means how close a measurement is to the true value. Precision means how consistent repeated measurements are. You can be precise without being accurate if your results are close together but far from the correct value.

*6. What are significant figures?*

Significant figures are the digits in a number that carry meaning about its precision. They show how exact a measurement is. For example, 2.50 has three significant figures, meaning it's measured more precisely than 2.5.

*7. Explain why water evaporates faster on a hot, sunny day.*

On a hot, sunny day, more energy from the sun is absorbed by water molecules. This increases their motion, helping them escape into the air as vapor. On a cold, cloudy day, less energy is available, so evaporation is slower.

*8. Which beaker has greater average kinetic energy?*

Beaker B (37°C) has greater average kinetic energy because temperature is directly related to how fast molecules move. Higher temperature = faster motion = more kinetic energy.

*9. What is the difference between a physical change and a chemical change?*

A physical change alters the form but not the identity (e.g., melting ice). A chemical change creates a new substance (e.g., rusting iron).

*10. What does a good hypothesis require?*

A good hypothesis is testable and based on observations. It should make a clear prediction that can be proven true or false through experiments.

*11. Classify the statements:*

a. Law - It describes a natural tendency.

b. Observation - It describes physical properties.

c. Observation - It describes how bases feel.

d. Hypothesis - It predicts an outcome based on behavior.

*12. What is a control? What is a variable?*

A control is the part of an experiment that stays the same. A variable is what you change or measure. Controls help you compare results fairly.

*13. Explain the relationship between models and theories.*

Models are simplified representations used to explain or visualize theories. Theories are broader explanations; models help test or demonstrate them.

*14. Why is conservation of energy a law, not a theory?*

It's a law because it has been repeatedly observed and confirmed. It describes a consistent rule in nature, not just an explanation.

*15. Why is it important to keep track of significant figures?*

They show how precise your measurements are. Using the correct number avoids false accuracy and keeps calculations honest.

*16. Significant figures in math:*

a. When adding, the result should match the number with the fewest decimal places.

b. When multiplying, the result should match the number with the fewest total significant figures.

*17. Calculations with significant figures:*

a. 2.145 + 0.002 = *2.147* (4 sig figs)

b. (9.8 × 8.934) + 0.0048 = 87.5532 + 0.0048 = *87.56* (3 sig figs)

c. (172.56 / 43.8) − 1.825 = 3.9404 − 1.825 = *2.12* (3 sig figs)

*18. Which statements contain exact numbers?*

a. Exact - 12 eggs in a dozen is a defined quantity.

b. Not exact - "over 140 km/h" is an estimate.

c. Not exact - 21 people is counted but not defined.

d. Not exact - 40,000 km is rounded.

*19. Scientific notation for 743,000,000:*

a. One sig fig: *7 × 10⁸*

b. Two sig figs: *7.4 × 10⁸*

c. Four sig figs: *7.430 × 10⁸*

You got it, Amy! Here's the rest of the questions answered in the same format — clear, simple, and with explanations. Each answer is marked with

and separated by

between different questions.

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*20. How many significant figures are there in each of the following measurements?*

a. 0.4004 mL → *4 sig figs* (zeros between and after digits count)

b. 6000 g → *1 sig fig* (unless there's a decimal, trailing zeros don't count)

c. 1.000 30 km → *6 sig figs* (all digits including zeros after decimal count)

d. 400 mm → *1 sig fig* (no decimal, so trailing zeros don't count)

*21. Calculate the sum of 6.078 g and 0.3329 g.*

6.078 + 0.3329 = *6.4109 g, but we round to 3 decimal places (least precise value), so the answer is 6.411 g*

*22. Subtract 7.11 cm from 8.2 cm.*

8.2 − 7.11 = *1.09 cm, but we round to 1 decimal place (least precise value), so the answer is 1.1 cm*

*23. What is the product of 0.8102 m and 3.44 m?*

0.8102 × 3.44 = *2.787088 m², round to 3 sig figs (least precise value), so the answer is 2.79 m²*

*24. Divide 94.20 g by 3.167 22 mL.*

94.20 ÷ 3.16722 = *29.74 g/mL, round to 4 sig figs (least precise value), so the answer is 29.74 g/mL*

*25. How many grams are in 882 μg?*

882 μg = *0.000882 g* (move decimal 6 places to the left since 1 g = 1,000,000 μg)

*26. Density of gold is 19.3 g/cm³*

a. Volume = mass ÷ density = 715 g ÷ 19.3 g/cm³ = *37.0 cm³*

b. If it's a cube: edge = ∛volume = ∛37.0 ≈ *3.33 cm*

*27. Specific heat calculation*

Q = mcΔT → 48 J = 35 g × c × (313 − 298)

→ 48 = 35 × c × 15 → c = 48 ÷ (35 × 15) = *0.0914 J/g·K*

*28. Energy needed to heat aluminum*

Q = mcΔT → Q = 75 × 0.897 × (94.6 − 22.4)

→ Q = 75 × 0.897 × 72.2 = *4,857 J*

*29. Final temperature of water*

Q = mcΔT → 420 = 35 × 4.18 × (Tf − 10)

→ 420 = 146.3 × (Tf − 10) → Tf − 10 = 420 ÷ 146.3 ≈ 2.87

→ Tf = *12.9°C*

*30. Write in scientific notation*

a. 0.0006730 → *6.730 × 10⁻⁴*

b. 50,000.0 → *5.00000 × 10⁴*

*31. Write in ordinary notation*

a. 7.050 × 10⁻³ g → *0.007050 g*

b. 4.00005 × 10⁷ mg → *40,000,500 mg*

*32. Perform operation in scientific notation*

(6.12433 × 10⁶) ÷ (7.15 × 10⁻³) = *8.564 × 10⁸* (rounded to 4 sig figs)

*33. Eliminate placeholder zeros*

a. 7500 → *7.5 × 10³*

b. 92,002,000 → *9.2002 × 10⁷*

*34. Significant figures in multiplication*

(1.36 × 10⁻⁵) × (5.02 × 10⁻²) → Answer has *3 sig figs* (least precise value)

*35. Copper alloy heat*

a. Q = mcΔT → 523 = 85 × c × (45 − 30) → c = 523 ÷ (85 × 15) = *0.410 J/g·°C*

b. Q = mcΔT → Q = 85 × 0.410 × (45 − 25) = *697 J*

*36. Volume of building*

Volume = length × width × height = 107 × 31 × 425 = *1,409,725 m³*

→ Scientific notation: *1.41 × 10⁶ m³*

*37. Density of object*

Density = mass ÷ volume = 57.6 ÷ 40.25 = *1.43 g/cm³*

*38. Convert 0.947 mg to grams and kilograms*

- Grams: 0.947 mg = *0.000947 g*

- Kilograms: 0.000947 g = *9.47 × 10⁻⁷ kg*

*39. Write in long form*

a. 4.5 × 10³ g → *4500 g*

b. 6.05 × 10⁻³ m → *0.00605 m*

c. 3.115 × 10⁶ km → *3,115,000 km*

*40. Write in scientific notation*

a. 800,000,000 m → *8 × 10⁸ m*

b. 0.00095 m → *9.5 × 10⁻⁴ m*

c. 60,200 L → *6.02 × 10⁴ L*

d. 0.0015 kg → *1.5 × 10⁻³ kg*

*41. Scientific notation calculations*

a. 37,000,000 × 7,100,000 = 2.627 × 10¹⁴

b. 0.000312 ÷ 486 = 6.42 × 10⁻⁷

c. (4.6 × 10⁴) × (7.5 × 10³) = 3.45 × 10⁸ cm²

*42. Significant figures in calculations*

a. 15.75 × 8.45 = *133.1 m²* (3 sig figs)

b. 5650 ÷ 27 = *209 L/min* (2 sig figs)

c. 6271 ÷ 59.7 = *105 m/s* (3 sig figs)

*43. Why is "the sun sets in the west" a law?*

It's a law because it's a consistent, observable pattern that happens every day due to Earth's rotation.

*44. Fertilizer experiment*

- Variable: Type of fertilizer

- Controls: Soil, water, sunlight, radish type

- Measure: Growth rate, size, health of radishes

*45. Graduated cylinder not calibrated*

It would affect accuracy because the measurements wouldn't reflect the true value. It could still be precise if repeated results are consistent, but they'd all be wrong.

*47. Valid experiment components*

You need a clear hypothesis, controlled variables, a control group, accurate measurements, and repeatable procedures.

*48. Limitations of thumb-width inch*

People's thumbs vary in size, so it's not a reliable or consistent unit. It lacks standardization, which is key for accurate measurement.

*49. Procedure to find specific heat of a metal*

1. Measure mass of metal

2. Heat it to known temperature

3. Drop it into water of known mass and temperature

4. Measure final temperature

5. Use Q = mcΔT to solve for specific heat

*50. Observation practice*

Watch for things like rust forming, ice melting, or gas bubbles in soda. Choose 3, research them, and explain using chemistry concepts.

*51. Energy transformations*

- Light → Chemical (photosynthesis)

- Chemical → Mechanical (eating food then moving)

- Electrical → Light → Heat (lamp)

→ Example: Solar panel → battery → fan

*52. Concept map terms*

- Start with *energy* in the center

- Branch to *endothermic* and