AFCT General Science: Physical and Chemical 2 — Questions and Answers

Question 1: What is Newton's Second Law of Motion?

An object at rest stays at rest unless acted upon by a force
Force equals mass times acceleration (F = ma) (Correct answer)
For every action there is an equal and opposite reaction
Energy cannot be created or destroyed

Correct answer: Force equals mass times acceleration (F = ma)

Newton's Second Law states that the net force acting on an object equals its mass multiplied by its acceleration (F = ma). This means acceleration is directly proportional to force and inversely proportional to mass.

Newton's Second Law of Motion (F = ma) is the most quantitative of the three laws. It states that the acceleration of an object is directly proportional to the net force applied and inversely proportional to its mass. Force is measured in newtons (N), where 1 N = 1 kg·m/s². If you double the force on an object, its acceleration doubles. If you double the mass, acceleration halves for the same force. The 'net force' is the vector sum of all forces acting on the object. For example, a 10 kg object with a net force of 50 N accelerates at 5 m/s². This law also applies to deceleration (negative acceleration). Newton's First Law (inertia) is actually a special case of the Second Law where F = 0, resulting in a = 0 (no change in velocity). The Second Law forms the foundation of classical mechanics and is used to analyze everything from projectile motion to orbital mechanics.

Question 2: What is the difference between an element and a compound?

Elements contain only one type of atom; compounds contain two or more types of atoms chemically bonded together (Correct answer)
Elements are always solids; compounds are always liquids
There is no difference between them
Elements are found in nature; compounds are only made in laboratories

Correct answer: Elements contain only one type of atom; compounds contain two or more types of atoms chemically bonded together

An element is a pure substance consisting of only one type of atom (e.g., oxygen, gold, carbon). A compound is a substance formed when two or more different elements chemically bond together in fixed proportions (e.g., water H2O, salt NaCl).

Elements are the simplest pure substances, each defined by its atomic number (number of protons). The 118 known elements are organized in the periodic table. An element cannot be broken down into simpler substances by chemical means. Compounds form when atoms of different elements bond in fixed ratios through ionic bonds (electron transfer, as in NaCl) or covalent bonds (electron sharing, as in H2O). Compounds have properties distinct from their constituent elements; for example, sodium (a reactive metal) and chlorine (a toxic gas) combine to form table salt. Compounds can be decomposed into their elements through chemical reactions, electrolysis, or thermal decomposition. Mixtures, in contrast, combine substances physically without chemical bonding, so components retain their individual properties and can be separated by physical means (filtration, distillation, etc.).

Question 3: What is the law of conservation of energy?

Energy always decreases in a closed system
Energy can be created by nuclear reactions
Energy cannot be created or destroyed, only transformed from one form to another (Correct answer)
Energy is conserved only in chemical reactions

Correct answer: Energy cannot be created or destroyed, only transformed from one form to another

The law of conservation of energy (First Law of Thermodynamics) states that the total energy in an isolated system remains constant. Energy can change forms (kinetic, potential, thermal, chemical, etc.) but the total amount is conserved.

The conservation of energy is one of the most fundamental principles in physics. Energy exists in many forms: kinetic (motion), potential (position or configuration), thermal (heat), chemical (bonds), electrical, nuclear, radiant (light), and sound. Energy continuously transforms between these forms but is never created or destroyed. A swinging pendulum converts between kinetic and potential energy. A car engine converts chemical energy (fuel) to thermal energy (combustion) to kinetic energy (motion) with some lost as waste heat and sound. In nuclear reactions, mass itself converts to energy per Einstein's E = mc², but mass-energy combined is still conserved. The Second Law of Thermodynamics adds that energy transformations are never 100% efficient; some energy always becomes unavailable thermal energy (entropy increases), which is why perpetual motion machines are impossible.

Question 4: What is the pH scale used to measure?

Temperature of a solution
The acidity or alkalinity of a solution (Correct answer)
The density of a liquid
The electrical conductivity of water

Correct answer: The acidity or alkalinity of a solution

The pH scale (0-14) measures how acidic or basic (alkaline) a solution is. Values below 7 are acidic, 7 is neutral, and above 7 is basic. The scale is logarithmic, so each unit represents a tenfold change in hydrogen ion concentration.

pH stands for 'potential of hydrogen' and is defined as the negative logarithm of hydrogen ion (H+) concentration: pH = -log[H+]. The scale runs from 0 (most acidic) to 14 (most basic/alkaline), with 7 being neutral (pure water). Because the scale is logarithmic, a pH of 3 is ten times more acidic than pH 4 and one hundred times more acidic than pH 5. Strong acids (HCl, H2SO4) have pH near 0-1; stomach acid is about pH 1.5-3.5; lemon juice is pH 2; coffee is pH 5; blood is pH 7.35-7.45 (slightly basic); baking soda is pH 9; ammonia is pH 11; and strong bases (NaOH) approach pH 14. Buffers resist pH changes and are essential in biological systems. Blood pH is tightly regulated; even small deviations (acidosis below 7.35 or alkalosis above 7.45) can be life-threatening.

Question 5: What is the difference between heat and temperature?

There is no difference; they are the same thing
Heat is the total thermal energy transferred between objects; temperature measures the average kinetic energy of particles (Correct answer)
Temperature measures heat content; heat measures molecular speed
Heat applies only to gases; temperature applies to all states of matter

Correct answer: Heat is the total thermal energy transferred between objects; temperature measures the average kinetic energy of particles

Heat is the transfer of thermal energy between objects of different temperatures. Temperature measures the average kinetic energy of particles in a substance. A large object at a low temperature can contain more total thermal energy than a small object at a high temperature.

Temperature is an intensive property (independent of amount) that measures the average kinetic energy of particles in a substance. It is measured in Celsius, Fahrenheit, or Kelvin scales. Heat (Q) is an extensive property—the transfer of thermal energy from a hotter object to a cooler one. Heat transfer occurs through conduction (direct molecular contact), convection (fluid circulation), and radiation (electromagnetic waves). The amount of heat needed to change an object's temperature depends on its mass, specific heat capacity (c), and temperature change: Q = mcΔT. For example, water has a high specific heat capacity (4.186 J/g°C), meaning it requires significant energy to change its temperature, moderating coastal climates. At phase changes (melting, boiling), heat is absorbed or released (latent heat) without temperature change as energy restructures molecular bonds rather than increasing molecular speed.

Question 6: What type of chemical bond involves the sharing of electron pairs between atoms?

Ionic bond
Covalent bond (Correct answer)
Metallic bond
Hydrogen bond

Correct answer: Covalent bond

A covalent bond forms when two atoms share one or more pairs of electrons to achieve stable electron configurations. These bonds commonly form between nonmetal atoms and are the basis of molecular compounds.

Covalent bonds form when atoms share electron pairs, typically between nonmetals with similar electronegativities. A single bond shares one pair (e.g., H-H), a double bond shares two pairs (e.g., O=O), and a triple bond shares three pairs (e.g., N≡N). Bond strength increases with bond order. In nonpolar covalent bonds, electrons are shared equally (e.g., O2, N2). In polar covalent bonds, electrons are shared unequally due to different electronegativities, creating partial charges (e.g., H2O, where oxygen pulls electrons more strongly). This contrasts with ionic bonds, where electrons are fully transferred from metal to nonmetal (e.g., Na donates an electron to Cl in NaCl). Metallic bonds involve a 'sea of electrons' shared among metal atoms. Hydrogen bonds are weak intermolecular attractions between a hydrogen atom bonded to an electronegative atom (N, O, F) and another electronegative atom, crucial in water properties and DNA structure.

AFCT General Science: Physical and Chemical 2

What is Newton's Second Law of Motion?