3.3 Temperature

Definition and Measurement

Temperature is a measure of how hot or cold an object is compared to another object. It is measured using a thermometer.

• Key Point: Temperature quantifies thermal energy.

• Example: Measuring body temperature with a clinical thermometer.

Temperature Scales

Temperature can be measured in different scales, including Celsius (°C), Fahrenheit (°F), and Kelvin (K).

• Key Point: The Kelvin scale is the SI unit for temperature.

• Formula:

• Example: Normal body temperature (37°C) in Kelvin: K

3.4 Energy

Definition of Energy

Energy is the ability to do work or produce heat. It makes objects move and is essential for physical and chemical processes.

• Key Point: Energy is required for all forms of life and mechanical functions.

• Example: A defibrillator provides electrical energy to restore normal heart rhythm.

Kinetic Energy

Kinetic energy is the energy of motion. Examples include:

• Swimming

• Water flowing over a dam

• Working out

Potential Energy

Potential energy is stored energy, available for use at a later time. It is determined by the position of an object or its chemical composition.

• Examples: Water at the top of a dam, chemical bonds in food, a compressed spring.

• Potential energy can be converted to kinetic energy (e.g., water flowing down a dam).

Heat and Energy

Heat is the energy associated with the movement of particles. It flows from a hotter object to a colder one.

• When an ice cube is added to water, heat flows from the water to the ice, causing the ice to melt.

• Heat is measured in joules (J) or calories (cal).

Units of Energy

Energy is measured in:

• Joule (J): SI unit of energy.

• Calorie (cal): Amount of energy needed to raise the temperature of 1 g of water by 1°C.

• Conversion:

3.5 Energy and Nutrition

Energy in Food

One hour of swimming uses approximately 2000 kJ of energy.

• Nutritionists use a calorimeter to measure the energy released from food.

• On food labels, energy is shown as Calories (with a capital C), where 1 Calorie = 1000 calories = 1 kilocalorie (kcal).

Calorimeters

Calorimeters measure the heat released from burning food samples to determine the energy value of the food.

• Used in nutritional science to calculate energy content.

Chemistry Link to Health: Weight Loss

The number of calories needed for daily energy expenditure varies by age, gender, and activity level.

3.6 Specific Heat

Definition

Specific heat (C) is the amount of heat needed to raise the temperature of exactly 1 g of a substance by 1°C.

• Different substances have different specific heats.

• Formula:

• Where = heat (J), = mass (g), = specific heat (J/g°C), = change in temperature (°C).

Specific Heats of Some Substances

Calculations Using Specific Heat

To calculate the heat gained or lost by a substance:

• Use the formula

• Example: If the specific heat of 24.8 g of metal absorbs 275 J of energy and the temperature rises from 20.2°C to 24.5°C, solve for C.

3.7 Changes of State

Melting and Freezing

Melting is the change from solid to liquid at its melting point. Freezing is the change from liquid to solid at its freezing point.

• Both are reversible processes.

Sublimation and Deposition

Sublimation is the change from solid directly to gas. Deposition is the change from gas directly to solid.

• Example: Dry ice (solid CO2) sublimes at -78°C.

• Used to prepare freeze-dried foods for long-term storage.

Evaporation, Boiling, and Condensation

Evaporation occurs when molecules at the surface gain enough energy to form a gas. Boiling occurs when all molecules acquire enough energy to form a gas throughout the liquid. Condensation is the change from gas to liquid.

Heat of Vaporization

The heat of vaporization is the amount of energy required to convert 1 g of liquid to gas at its boiling point.

• Vaporization and condensation are reversible processes.

5.1 Natural Radioactivity

Definition and Sources

Radioactivity is the emission of particles or energy from unstable atomic nuclei. It occurs naturally in some elements, such as uranium and radium.

• Alpha (α), beta (β), and gamma (γ) radiation are common forms.

Radioisotopes

A radioisotope is an isotope of an element that emits radiation. It has an unstable nucleus and decays over time.

• Example: Iodine-131 used in medical diagnostics.

Some Forms of Radiation

Biological Effects of Radiation

Radiation can damage cells and tissues, causing chemical changes and increasing cancer risk. Different types of radiation penetrate tissues to different depths.

Radiation Protection

• Use protective clothing and shielding.

• Limit exposure time and increase distance from the source.

Properties of Radiation

5.3 Radiation Measurement

Measuring Radiation

Radiation levels are measured using devices such as Geiger counters and dosimeters.

• Units include becquerel (Bq) for activity and gray (Gy) for absorbed dose.

• Sievert (Sv) measures biological effects.

Dosimeters

Dosimeters measure radiation exposure for individuals working with radioactive materials.

• They detect and record exposure to gamma rays, beta particles, etc.

States: Average Annual Radiation Exposure

5.5 Medical Applications Using Radioactivity

Radioisotopes in Medicine

Radioisotopes with short half-lives are used in nuclear medicine to diagnose and treat diseases.

• They emit radiation that can be detected by imaging devices.

• Example: Scans with radioactive iodine-131 in the thyroid.

Scans with Radioisotopes

Radioisotope scans help visualize organ function and detect abnormalities.

• Commonly used in thyroid, bone, and cardiac imaging.

Additional info: All tables and some examples inferred from slide images for completeness.