Chem 1310 Problems

How to Solve

How to find amount of atoms in a molecule

1. Find the percentage of the element present in one mol of molecule

2. Multiply by the mass of the molecule given

3. Convert mass of element to mol

4. Multiply mol by the subscript of the molecule

5. Convert mol to atoms by multiplying by 6.022 × 10²³

How to find unknown percent abundance

1. Subtract percentage of known isotopes to find percent of unknown isotopes (n)

2. Set given isotope abundance to x

3. Multiply each isotope by percent abundance, including (n -x) and x

4. Set equation equal to average atomic mass and solve for x

Calculate number of atoms of element in molecule based on molecule composition

1. Calculate molar mass of compound based on given information

2. Set up percentage equation based on x

3. Solve for x

Find mass required for percentage yield

1. Utilize given actual value to find theoretical value

2. Convert theoretical value to mol

3. Find mol necessary of reactant to create that much product

Find change in internal energy for a given system based on pressure

1. Use the law of thermodynamics to find change in energy = q + w, where work = -pressure x change in volume

2. Calculate change in volume for the system

3. Plug in given pressure and change in volume to find work

4. Plug given values to find change in energy

Find change in heat for a coffee cup calorimeter

m_c c (T_hot - T_final) = m_col c (T_final - T_cold) + c_cal (T_f - T_cold)

Determine heat of reaction

1. Cancel out compounds necessary to get final reaction

2. When reversing reactions, multiple deltaH by -1

3. When multiplying reactions by c, multiplye deltaH by c

4. Add the new deltaH for each reaction to determine overeall heat of reaction

How to find mol of a compound for a gas reaction

1. Use ideal gas law to find mol of gas

2. Use stoichiometric relationship to find mol of solid

How to find heat of reaction

1. Divide given deltaH by deltaH of reaction

2. Find stoichiometric ratio between mol of reaction and mol of element A

3. Multiply mol of A by molar mass of A to find necessary A

How to find partial pressure

1. Find total number of moles

2. Utilize the relationship pressure ratio = mol ratio to find partial pressure for given substance

3. Subtract P_i from P_total to find P of the other compound

Calculate wavelength of transition state

1. Find the difference between each transition state

2. Convert eV to Joules

3. Use energy-wavelength relation to find wavelength of transition

Calculate moles of photon in laser pulse

1. Calculate E_photon

2. Find number of photons in laser beam by dividing E_beam by E_photon

3. Divide number of photons by Avogadro’s number

Calculate time for decomposition

1. Find fraction of compound decomposed

2. Plug in given mass into integrated rate law

3. Find time necessary for decomposition

Solve for constant of equilibrium for pressure

1. Find the molarity of gas

2. Create an ice table to find x based on the starting numbers

3. Convert found equilibrium values to partial pressures

4. Solve for K_p

5. Find the partial pressures based on the value of x

6. Add partial pressures together