Chapter 12 Chemical Reactions: Fast and Slow Flashcards
Signs That a Chemical Reaction has taken place (6)
- A change in colour.
- A change in temperature.
- The production of light.
- The emission of sound.
- A distinctive smell.
- Bubbles of gas being produced ( called effervesence).
Exothermic Reactions and Endothermic Reactions
Exothermic reactions give out heat. The temperature of the surroundings increases.
Endothermic reactions take in heat. The temperature of the surroundings decreases.
Energy Profile Diagams
Diagrams which show the energy stored in the reactants compared to the energy stored in the products.
Collision Theory
Before a chemical reaction happens the particles of the reactants must collide with each other.
Activation Energy
The minimum energy neede to start a reaction.
Methods of measuring how much product is formed in a certain time (3).
- Monitor the production of gas.
- Monitor the temperature changes during a reaction.
- Monitor the appearance of the reactantsand the products during the reaction.
How temperature effects the rate of reaction
Particles have more energy at higher temperatures. So when particles collide they are more likely to have enough energy to react with each other. Raising the temperature by 10°C doubles the rate of many reactions.
How concentration effects the rate of reaction
As there are more particles in concentrated solutions, there are more collisions. These collisions increase the rate of reaction.
How surface area effects the rate of reaction
As particle size gets smaller the surface area increases. Surface area is the measure of how much a substance is exposed. The larger the surface area, the greater the area available for collisions to take place. Increasing the surface area increases the rate of reaction.
How catalysts effect the rate of reaction
A catalyst is a substance which speeds up a chemical reaction. At the end of the reaction, a catalyst is chemically unchanged, meaning it can be used over and over again. A catalyst works by lowering the amount of energy needed for a reaction to happen. Catalysts make it easier for particles to react, as they will need less energy to get over the barrier.
Name the three ways that a gas can be collected
- Downward Displacement of Air
- Upward Displacement of Air
- Over Water
Explain Downward Displacement of Air
Can be used for a gas that is heavier than air. The gas produced sinks to the bottom of the flask and air is pushed out the top as the flask is filled with the gas.
Explain Upward Displacement of Air
Can be used for a gas that is lighter than air. The gas produced moves to the top of the flask and air is pushed out the bottom as the flask is filled with the gas.
Explain Over Water Method
Can be used to collect gases that do not dissolve in water. You will easily see when the jar is full of the new gasas there will be no water left in the jar.
Decomposition Reactions
A reaction where a substance is broken down into simpler substances. E.g: hydrogen peroxide into water and oxygen.
Heat is often used to bring about decomposition. Catalysts such as manganese dioxide and catalase can be added to speed this up.
