level: 6.4 Hess's law
Questions and Answers List
level questions: 6.4 Hess's law
| Question | Answer |
|---|---|
| What does law of conservation of energy state and what is it also called? | Energy cannot be created or destroyed Also called first law of thermodynamics |
| What does Hess's law state? | the total enthalpy change in a chemical reactions is independent of the route by which chemical reaction takes place as long as the initial and final conditions are the same |
| We use enthalpy changes of formation of reactants and products to calculate what? | To calculate enthalpy change of reaction |
| We take note of the direction of arrow to find the one-stage (Direct or indirect) and 2-stage (Direct or indirect) routes | 1. Direct 2. Indirect |
| To calculate the enthalpy changes of reaction using this type of enthalpy cycle, we use the following procedure (Enthalpy change of formation) | 1. Write the balanced equation at the top 2. Draw cycle with elements at the bottom 3. Draw in all arrows, making sure they go in correct directions 4. Apply Hess's law, taking into account the number of moles of each each reactant and product |
| When doing enthalpy cycle (energy cycle) calculations remember that... (2) | - The enthalpy change of an element in its normal state is zero - You must take into account the number of moles of reactants and products in each part of energy cycle |
| Use enthalpy change of combustion of reactants and products to calculate what? | To calculate |