Changes Around Us: Physical and Chemical – Formula & Equation Sheet
Essential formulas and equations from Curiosity, tailored for Class 7 in Science.
This one-pager compiles key formulas and equations from the Changes Around Us: Physical and Chemical chapter of Curiosity. Ideal for exam prep, quick reference, and solving time-bound numerical problems accurately.
Key concepts & formulas
Essential formulas, key terms, and important concepts for quick reference and revision.
Formulas
E = mc²
E represents energy (in joules), m is mass (in kg), and c is the speed of light (≈ 3 × 10⁸ m/s). This formula shows how mass can be converted into energy, a foundational idea in Einstein’s theory of relativity.
Q = mcΔT
Q indicates heat energy (in joules), m is mass (in kg), c is specific heat capacity (J/kg·°C), and ΔT is the change in temperature (in °C). This formula determines the amount of heat required to change the temperature of a substance.
p = m/V
p is density (kg/m³), m is mass (in kg), and V is volume (in m³). This formula relates mass and volume to calculate the density of a substance.
R = ρL/A
R is resistance (in ohms), ρ is resistivity (Ω·m), L is length of the conductor (in m), and A is cross-sectional area (in m²). This formula finds the resistance of a conductor based on its material and dimensions.
C = Q/V
C represents capacitance (in farads), Q is charge (in coulombs), and V is voltage (in volts). It is used to determine the ability of a system to store electrical energy.
V = IR
V is voltage (in volts), I is current (in amperes), and R is resistance (in ohms). This formula defines the relationship between current and voltage in a circuit.
PV = nRT
P is pressure (in pascals), V is volume (in m³), n is the amount of substance (in moles), R is the ideal gas constant, and T is temperature (in kelvins). This equation explains the relationship in an ideal gas.
ΔS = ΔH/T
ΔS is entropy change (J/K), ΔH is enthalpy change (in joules), and T is temperature (in kelvins). This formula relates the changes in entropy to enthalpy and temperature.
H₂ + O₂ → 2H₂O
This chemical equation represents the reaction between hydrogen and oxygen to form water. It shows the conservation of mass in chemical reactions.
Fe + O₂ → Fe₂O₃
This equation represents the rusting process where iron reacts with oxygen to produce iron oxide, commonly known as rust.
Equations
Lime water test: Ca(OH)₂ + CO₂ → CaCO₃ + H₂O
This equation represents the reaction in which lime water (calcium hydroxide) reacts with carbon dioxide to form calcium carbonate (a cloudy precipitate) and water.
Vinegar + Baking soda → CO₂ + Other substances
This reaction produces carbon dioxide gas when vinegar reacts with baking soda, resulting in bubbling and fizzing.
Mg + O₂ → MgO + Heat + Light
This equation shows the combustion of magnesium in oxygen, producing magnesium oxide along with the release of heat and light.
H₂O (l) → H₂O (g)
This equation signifies the physical change of water from liquid (l) to gas (g) through evaporation.
C₃H₈ + 5O₂ → 3CO₂ + 4H₂O + Heat
This is the combustion reaction of propane (C₃H₈) in oxygen that produces carbon dioxide and water, releasing energy in the form of heat.
4Fe + 3O₂ → 2Fe₂O₃
This equation describes the formation of rust, where iron reacts with oxygen to form iron oxide.
CaCO₃ → CaO + CO₂
This equation shows the thermal decomposition of calcium carbonate into calcium oxide and carbon dioxide upon heating.
2H₂ + O₂ → 2H₂O
This balanced reaction indicates the synthesis of water from hydrogen and oxygen, highlighting the conservation of mass.
N₂ + 3H₂ → 2NH₃
This equation represents the synthesis of ammonia, a crucial process in chemistry, emphasizing stoichiometry in reactions.
C₁₂H₂₂O₁₁ + H₂O → 2C₆H₁₂O₆
This equation describes the hydrolysis of sucrose (table sugar) into glucose, demonstrating the chemical change during digestion.
