Chemistry Conversions Cheat Sheet
Navigating the world of chemistry often requires converting between units, whether it’s mass to moles, volume to mass, or energy to temperature. This cheat sheet provides a comprehensive guide to essential chemistry conversions, ensuring you have the tools to tackle any problem. From the basics of dimensional analysis to the intricacies of gas laws, this resource is designed to simplify your calculations.
1. Mass-Mole Conversions
Converting between mass and moles is foundational in stoichiometry. Use the molar mass (g/mol) as the conversion factor.
Formula:
[
\text{moles} = \frac{\text{mass (g)}}{\text{molar mass (g/mol)}}
]
[
\text{mass (g)} = \text{moles} \times \text{molar mass (g/mol)}
]
Example:
Convert 10.0 g of water (H₂O) to moles.
[
\text{Molar mass of H₂O} = 18.02 \, \text{g/mol}
]
[
\text{moles} = \frac{10.0 \, \text{g}}{18.02 \, \text{g/mol}} = 0.555 \, \text{moles}
]
2. Mole-Particle Conversions
Avogadro’s number (6.022 × 10²³ particles/mol) is the bridge between moles and particles (atoms, molecules, or ions).
Formula:
[
\text{particles} = \text{moles} \times 6.022 \times 10^{23}
]
[
\text{moles} = \frac{\text{particles}}{6.022 \times 10^{23}}
]
Example:
Convert 2.0 moles of helium (He) to atoms.
[
\text{atoms} = 2.0 \, \text{moles} \times 6.022 \times 10^{23} = 1.204 \times 10^{24} \, \text{atoms}
]
3. Volume-Mass Conversions (Density)
Density (g/mL or g/cm³) allows conversion between mass and volume.
Formula:
[
\text{mass (g)} = \text{volume (mL)} \times \text{density (g/mL)}
]
[
\text{volume (mL)} = \frac{\text{mass (g)}}{\text{density (g/mL)}}
]
Example:
Convert 500 mL of water to grams (density = 1.0 g/mL).
[
\text{mass} = 500 \, \text{mL} \times 1.0 \, \text{g/mL} = 500 \, \text{g}
]
4. Gas Law Conversions
The ideal gas law (PV = nRT) is essential for converting between pressure, volume, temperature, and moles of gas.
Common Conversions:
- STP Conditions: 1 mole of gas = 22.4 L at 0°C and 1 atm.
- Temperature: Convert between Kelvin (K) and Celsius (°C):
[
K = °C + 273.15
]
- Pressure: Convert between atm, mmHg, and kPa:
[
1 \, \text{atm} = 760 \, \text{mmHg} = 101.3 \, \text{kPa}
]
Example:
Convert 3.0 moles of gas at STP to volume.
[
\text{Volume} = 3.0 \, \text{moles} \times 22.4 \, \text{L/mol} = 67.2 \, \text{L}
]
5. Energy Conversions
Energy is often converted between joules (J), kilojoules (kJ), and calories (cal).
Conversion Factors:
[
1 \, \text{kJ} = 1000 \, \text{J}
]
[
1 \, \text{cal} = 4.184 \, \text{J}
]
Example:
Convert 500 kJ to calories.
[
\text{cal} = \frac{500,000 \, \text{J}}{4.184 \, \text{J/cal}} = 119,500 \, \text{cal}
]
6. Concentration Conversions
Concentration units like molarity (M), mass percent, and parts per million (ppm) require specific conversions.
Molarity (M):
[
\text{Molarity (M)} = \frac{\text{moles of solute}}{\text{liters of solution}}
]
Mass Percent:
[
\text{Mass \%} = \left( \frac{\text{mass of solute}}{\text{mass of solution}} \right) \times 100\%
]
Example:
Convert 250 mL of 0.5 M NaCl to grams of NaCl.
[
\text{moles of NaCl} = 0.250 \, \text{L} \times 0.5 \, \text{M} = 0.125 \, \text{moles}
]
[
\text{mass of NaCl} = 0.125 \, \text{moles} \times 58.44 \, \text{g/mol} = 7.30 \, \text{g}
]
7. Temperature Scales
Convert between Celsius (°C), Fahrenheit (°F), and Kelvin (K).
Formulas:
[
K = °C + 273.15
]
[
°F = \left( \frac{9}{5} \times °C \right) + 32
]
Example:
Convert 25°C to Kelvin.
[
K = 25 + 273.15 = 298.15 \, \text{K}
]
8. Dimensional Analysis
Dimensional analysis is the backbone of unit conversions. Multiply by conversion factors to cancel unwanted units.
Example:
Convert 50 miles to kilometers (1 mile = 1.609 km).
[
50 \, \text{miles} \times \frac{1.609 \, \text{km}}{1 \, \text{mile}} = 80.45 \, \text{km}
]
How do I convert grams to moles without a periodic table?
+If you don’t have a periodic table, use the formula: moles = mass (g) / molar mass (g/mol). Estimate the molar mass based on common elements (e.g., H = 1, C = 12, O = 16). For example, for H₂O, molar mass ≈ 18 g/mol.
What’s the difference between molarity and molality?
+Molarity (M) is moles of solute per liter of solution, while molality (m) is moles of solute per kilogram of solvent. Molarity depends on volume, which changes with temperature, whereas molality is temperature-independent.
How do I convert between gas volumes at different conditions?
+Use the combined gas law: \frac{P₁V₁}{T₁} = \frac{P₂V₂}{T₂}. Ensure temperatures are in Kelvin and pressures in consistent units (e.g., atm or kPa).
Why is Avogadro’s number important in chemistry?
+Avogadro’s number (6.022 × 10²³) links the macroscopic world (moles) to the microscopic world (atoms/molecules), enabling precise calculations in stoichiometry and reactions.
By mastering these conversions, you’ll streamline your problem-solving process and deepen your understanding of chemical principles. Practice regularly, and soon these calculations will become second nature!
