GCSE Chemistry Formula Sheet
📘 GCSE Chemistry Formula Sheet with Examples
All key chemistry equations with examples to help your revision! ✅
🧪 Moles & Concentration
Formula (Moles): \( n = \frac{\text{mass}}{\text{molar mass}} \)
Example: If the mass of a substance is 20 g and its molar mass is 10 g/mol, the number of moles is \( n = \frac{20}{10} = 2 \) moles.
Formula (Concentration): \( C = \frac{n}{V} \)
Example: If 2 moles of a substance are dissolved in 1 liter of solution, the concentration is \( C = \frac{2}{1} = 2 \) mol/L.🌬️ Gas Laws
Ideal Gas Law: \( PV = nRT \)
Example: If the pressure is 2 atm, the volume is 5 L, and the temperature is 300 K, the number of moles is \( n = \frac{PV}{RT} \).⚖️ Stoichiometry
Formula: Balance chemical reactions to find the amount of reactants/products.
Example: In the reaction \( 2H_2 + O_2 \rightarrow 2H_2O \), you can use stoichiometry to find how much water is produced.🧪 Acids & Bases
pH Formula: \( \text{pH} = -\log[\text{H}^+] \)
Example: If the concentration of hydrogen ions \( [\text{H}^+] \) is \( 1 \times 10^{-3} \) mol/L, then the pH is \( \text{pH} = -\log(1 \times 10^{-3}) = 3 \).
Neutralization: \( \text{Acid} + \text{Base} \rightarrow \text{Salt} + \text{Water} \)
Example: In the reaction between hydrochloric acid and sodium hydroxide, \( HCl + NaOH \rightarrow NaCl + H_2O \), hydrochloric acid and sodium hydroxide neutralize each other to form salt and water.⚡ Electrolysis
Faraday's Law: \( m = \frac{M \times I \times t}{n \times F} \)
Example: If the current is 2 A, the time is 10 s, and the number of electrons involved in the reaction is 1, the mass of substance deposited can be calculated.🔥 Energy Changes
Enthalpy Change: \( \Delta H = H(\text{products}) - H(\text{reactants}) \)
Example: In an exothermic reaction, the enthalpy change \( \Delta H \) will be negative, indicating that energy is released.⏳ Reaction Rates
Rate of Reaction: \( \text{Rate} = \frac{\Delta[\text{concentration}]}{\Delta t} \)
Example: If the concentration of a reactant changes by 0.5 mol/L in 2 seconds, the rate of reaction is \( \frac{0.5}{2} = 0.25 \) mol/L·s.💥 Bond Energy
Energy Change: \( \text{Energy change} = \text{Energy of bonds broken} - \text{Energy of bonds formed} \)
Example: In a reaction, if 500 kJ of energy is required to break bonds and 400 kJ is released when new bonds are formed, the net energy change is 100 kJ.🔬 Limiting Reactants
Formula: The reactant that runs out first, limiting the amount of product.
Example: In a reaction between hydrogen and oxygen to form water, if hydrogen is in excess, oxygen will be the limiting reactant.⚙️ Yield
Percentage Yield: \( \% \text{Yield} = \frac{\text{Actual Yield}}{\text{Theoretical Yield}} \times 100 \)
Example: If the actual yield of a reaction is 80 g and the theoretical yield is 100 g, the percentage yield is \( \frac{80}{100} \times 100 = 80\% \).💧 Solutions & Dilution
Dilution Formula: \( C_1 V_1 = C_2 V_2 \)
Example: If you dilute a 10 mol/L solution by adding water, and you want the final volume to be 5 L, the concentration is given by the formula.❄️ Thermodynamics
Gibbs Free Energy: \( \Delta G = \Delta H - T\Delta S \)
Example: In a spontaneous reaction, \( \Delta G \) must be negative.
Entropy Change: \( \Delta S = \frac{Q}{T} \)
Example: The entropy change in a system is the heat energy \( Q \) divided by the absolute temperature \( T \).🔥 Arrhenius Equation
Arrhenius Equation: \( k = A \times e^{-\frac{E_a}{RT}} \)
Example: This equation shows the relationship between the rate constant \( k \), activation energy \( E_a \), and temperature \( T \).🔋 Electrochemical Series
Standard Electrode Potential: \( E^\circ = E^\circ(\text{cathode}) - E^\circ(\text{anode}) \)
Example: For a redox reaction, the standard electrode potential determines the direction of the reaction.