Science Essentials: Temperature, Heat, Reactions, Environment

Understanding Temperature

What is Temperature?

Temperature is the measurement of a substance's thermal energy.

Measuring Temperature

Mercury Thermometer

A mercury thermometer consists of a bulb containing liquid mercury and a thin tube. The liquid expands due to thermal expansion and rises up the tube, allowing the temperature to be read on a calibrated scale.

Digital Thermometer

A digital thermometer uses a microprocessor that measures the temperature and displays it on a liquid crystal display (LCD).

Temperature Scales

Common temperature scales include Celsius (ºC) and Kelvin (ºK).

• Celsius to Kelvin: K = C + 273.15
• Kelvin to Celsius: C = K - 273.15

Heat Transfer Mechanisms

Conduction

Conduction is the transfer of heat energy primarily from solid to solid materials through direct contact.

• Thermal Conductor: Substances that efficiently transfer thermal energy from one point to another.
• Thermal Insulator: Substances that transfer thermal energy slowly from one point to another, resisting heat flow.

Convection

Convection is the process of heat transfer in fluids (liquids and gases) through the movement of convection currents, where warmer, less dense fluid rises and cooler, denser fluid sinks.

Radiation

Radiation is the process of heat transfer by which bodies emit energy that can move through a vacuum, without the need for a medium.

Fundamentals of Chemical Reactions

Key Components of Reactions

• Reactants: The initial substances that, when mixed together, start a chemical reaction.
• Products: The new substances that form as a result of a chemical reaction.

Law of Conservation of Mass

The Law of Conservation of Mass states that the total mass of the products is the same as the total mass of the reactants in a chemical reaction. Mass is neither created nor destroyed.

Balancing Chemical Equations

Balancing chemical equations ensures that the same number of atoms of each element are present in both the reactants and products, adhering to the Law of Conservation of Mass.

Types of Chemical Reactions

• Exothermic Reactions: Reactions that release thermal energy into the surroundings, often resulting in a temperature increase. (e.g., energy change of -580 kJ, indicating energy released)
• Endothermic Reactions: Reactions that absorb thermal energy from the surroundings, often resulting in a temperature decrease. (e.g., energy change of +580 kJ, indicating energy absorbed)

Rate of Chemical Reactions

Factors Affecting Reaction Rate

• Concentration of Reactants: Increasing reactant concentration generally increases the reaction rate.
• Temperature: Increasing temperature generally increases the reaction rate.
• Contact Area: Increasing the surface area of contact between reactants generally increases the reaction rate.

Defining Reaction Rate

Reaction rate is the speed at which reactants are consumed and products are formed during a chemical reaction.

The Greenhouse Effect and Climate Change

Causes and Impacts

Human activities, such as industrial processes and deforestation, produce significant amounts of greenhouse gases (primarily carbon dioxide). These gases trap radiation within Earth's atmosphere, leading to phenomena like global warming and climate change. Other environmental issues include acid rain and ozone layer depletion.