| A positive sign on a reaction pathway diagram shows | Endothermic reactions |
| Activation energy always has a positive value of enthalpy change, why? | Because enough energy has to be absorbed |
| Activation energy always has a positive value of enthalpy change, why? | Because enough energy has to be absorbed |
| A positive sign on a reaction pathway diagram shows | Endothermic reactions |
| Chemical reaction that transfer heat to surroundings are described as? | exothermic |
| Chemical reactions that absorb heat energy from surroundings are described as? | endothermic |
| In exothermic reactions, temperatures of surrounding increases. Theses surroundings include (4)? Give 3 examples of exothermic reactions. | Surroundings include
- Solvent
- Air around test -tube
- Test tube itself
- Anything dipping into the test-tube
Examples of exothermic reactions include
1. Combustion of fuels
2. Oxidation of carbohydrates in bodies of animals and plants (respiration)
3. Reaction of water with quicklime (calcium oxide) |
| What are 3 examples of endothermic reactions | 1. Decomposition of limestone by heating (all thermal decompositions are endothermic)
2. Photosynthesis
3. Dissolving certain ammonium salts in water |
| Energy change between a chemical reaction and its surroundings at constant pressure is called the | Enthalpy change |
| What is Enthalpy | Enthalpy is the total energy associated with materials that react |
| What is the symbol for enthalpy | H |
| Cannot measure enthalpy, but we can measure an enthalpy change when heat energy is exchanged with surroundings. We write this as: | Enthalpy change = change of product - enthalpy of reactants |
| What are the units for enthalpy change | kilojoules per mole (Kj mol^-1) |
| What are the diagrams called that show enthalpy changes? | Reaction pathway diagrams / enthalpy profile diagrams |
| On Reaction pathway diagrams what is shown on the y-axis and what is shown on the x-axis | y-axis = enthalpy of reactants and products
x-axis = Reaction pathway, wuth reactants on the left and products on the right |
| Reaction pathway diagrams usually also show (1) as a hump (up and down curve) between reactants and the product | Activation energy Ea |
| What is activation energy | Activation energy is the minimum energy that colliding particles must possess for a reaction to happen |
| Activation energy always has a positive value of enthalpy change, why? | Because enough energy has to be absorbed to increase the kinetic energy of reactant molecules so that they collide with enough force to break bonds |
| For exothermic reactions, enthalpy of reactants must be (< / >) the the enthapy of the products | Greater than |
| A negative sign on a reaction pathway diagram shows | Exothermic reactions |
| For endothermic reactions, the enthalpy of the product must be (< / >) than enthalpy of reactants | Greater than |
| A positive sign on a reaction pathway diagram shows | Endothermic reactions |
