Chemical reactions Flashcards
Define an exothermic change or reaction
heat energy is given out, including combustion reactions or explosions
Define an endothermic change or reactionr
heat energy is taken in, including photosynthesis or dissolving ammonium nitrate in water
Describe the breaking and making of bonds in relation to endothermic and exothermic as endothermic and the making of bonds as exothermic
breaking bonds is endothermic, making bonds is exothermic
the overall heat energy change for endothermic and exothermic reaction is:
a exothermic if more heat energy is released making bonds in the products than is required to break bonds in the reactants
b endothermic if less heat energy is released making bonds in the products than is required to break bonds in the reactants
a exothermic if more heat energy is released making bonds in the products than is required to break bonds in the reactants
b endothermic if less heat energy is released making bonds in the products than is required to break bonds in the reactants
Draw and interpret simple graphical representations
of energy changes occurring in chemical reactions (no
knowledge of activation energy is required)
look at exo and endo graphs
Investigate the effect of temperature, concentration and surface area of a solid on the rate of a reaction such as hydrochloric acid and marble chips
temperature: reactions happen faster when the temperature is higher. particles move faster at higher temperatures, so they collide more often and they also collide with more energy
surface area: reactions happen faster when solid reactants are broken up into smaller pieces. smaller pieces have a bigger surface area than the same mass of larger pieces, so there is more opportunity for collisions between reactants
concentration: reactions happen faster when more concentrated solutions are used. a more concentrated solution has more solute particles in a given volume. the more particles they are, the more likely they are to collide and react
describe the variation in chemical reactions
rates of chemical reactions vary from very fast, explosive reactions to very slow reactions
Describe the effect of changes in temperature, on the rate of reaction
temperature: reactions happen faster when the temperature is higher. particles move faster at higher temperatures, so they collide more often and they also collide with more energy
Describe how reactions can occur when particles collide and explain how rates of reaction are increased by increasing the frequency and/or energy of collisions
the particles need to collide with enough energy to make the reaction happen, so not all collisions result in a reaction. the higher the frequency of the collisions, and the higher the energy of the collisions, the faster the rate of reaction
Demonstrate an understanding that not all collisions
lead to a reaction, especially if particles collide with low
energy
not all collisions lead to a reaction if particles collide with low energy
Recall the effect of a catalyst on the rate of reaction
a catalyst speeds up a reaction without being used up
describe catalytic converters
> used in cars to reduce the pollution caused by waste gases from the engine. carbon monoxide and unburned fuel in the exhaust combine with oxygen to form carbon monoxide and water.
the platinum catalyst in catalytic converters is made into a fine mesh to give it a large surface area. this allows more of the waste gases to come into contact with the catalyst and so helps to speed up the reaction
catalytic converters work best at high temperatures.
Describe the effect of changes in surface area of a solid on the rate of reaction
surface area: reactions happen faster when solid reactants are broken up into smaller pieces. smaller pieces have a bigger surface area than the same mass of larger pieces, so there is more opportunity for collisions between reactants
Describe the effect of concentration, on the rate of reaction
concentration: reactions happen faster when more concentrated solutions are used. a more concentrated solution has more solute particles in a given volume. the more particles they are, the more likely they are to collide and react
