| What is an exothermic reaction? | 1)When energy is given out to the surroundings. Surroundings have more energy than they started with so temp increases.
2)More heat energy is released in making bonds in products than taken when breaking bonds in reactants |
| What is an endothermic reaction? | 1)When energy is taken in from the surroundings. The temperature of surroundings decreases
2)Less heat energy is released in making bonds in products than taken when breaking bonds in reactants |
| Give the required practical for temperature change. | 1)Place polystyrene cup in glass beaker to make it more stable.
2)Measure an appropriate volume of each liquid, eg 25 cm3.
3)Place one of the liquids in a polystyrene cup.
4)Record the temp of the solution
5)Add the second solution and record highest or lowest temp obtained
6)Change your independent variable and repeat the experiment. (Your independent variable could be the concentration of one of the reactants, or the type of acid/alkali being used, or the type of metal/metal carbonate being used.) |
| State weather this reaction is exothermic or endothermic (view pic) | Exothermic, overall change is negative, products have less energy than reactants |
| State weather this reaction is exothermic or endothermic (view pic) | Endothermic, overall change is positive, products have more energy than reactants |
| Hydrogen reacts with oxygen to form water:
2 × (H−H) + O=O → 2 × (H-O-H)
Use the bond energies in the table to calculate the energy change for this reaction.
Bond Bond energy
H−H 436 kJ mol-1
O=O 498 kJ mol-1
O-H 464 kJ mol-1 | Energy in = (2 x 436) + 498 = 1370 kJ mol -1
Energy out = 2 × 2 × 464 = 1856 kJ mol-1
Energy change = in - out = 1370 - 1856 = -486 kJ mol-1 |
