EDEXCEL GCSE Chemistry - Unit 2 - Topics 5+6

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What is an exothermic reaction?
In an exothermic reaction, chemical energy is transferred to heat energy, so the temperature rises.
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What is an endothermic reaction?
In an endothermic reaction, heat is taken in and transferred to chemical energy, so the temperature falls.
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How do all chemical reactions start?
All reactions start by breaking the bonds between the reactant atoms. Heat energy is needed to break bonds, so this is an endothermic process.
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What happens when bonds are made?
Energy is released when bonds are made, so making bonds is an exothermic process.
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Why do exothermic reactions happen?
In an exothermic reaction, less energy is needed to break the bonds in the reactants than is released in making bonds in the products. Therefore heat energy is released.
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Why do endothermic reactions happen?
In an endothermic reaction, more energy is needed to break the bonds in the reactants than is released in making bonds in the products. Therefore heat energy is absorbed.
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What is the collision theory?
An idea that relates collisions among particles to their reaction rates.
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When will the rate of any reaction increase?
The rate of any reaction will increase if the particles collide more frequently. Particles can only react with other particles when they collide, so the more often particles collide, the faster the reaction.
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What do the collisions between particles must have?
The collisions between particles must have enough energy to break the bonds in the reactants. The rate of reaction will be increased if there are more high-energy collisions because the particles are more likely to react when they collide.
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What happens to the rate of reaction when you increase the concentration of a reactant solution?
The more concentrated a solution, the more solute particles there are in a given volume.
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What does it mean when the concentration of a solution is increased?
This means that it is more likely that reactant particles will collide with one another - and the more collisions there are between reactant particles, the faster the rate of reaction will be.
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What happens to the rate of reaction when you increase the temperature of a reactant solution?
The higher the temperature, the faster the particles move. This means they collide with more energy and so are more likely to react.
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Why do particles collide more frequently when temperature is increased?
The particles move faster at higher temperatures and so collide more frequently. This means that increasing the temperature increases the rate of reactions.
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What happens to the rate of reaction when you increase the surface area?
The greater the surface area of a solid, the more particles there are at the surface. This means that there will be more frequent collisions between reactants and so a higher rate of reaction.
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What is the concentration of a solution?
The concentration of a solution is a measure of how much solute is dissolved in a solvent.
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What is the role of a catalyst?
A catalyst speeds up the rate of a reaction, but is not used up by the reaction.
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What is the role of catalytic converters in vehicles?
They reduce the amount of carbon monoxide and unburned fuel that come from the exhaust pipe.
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What makes a catalytic converter efficient?
The platinum in a catalytic converter is spread in a thin layer over a honeycomb ceramic structure to give a large surface area. This increases the number of reactions catalysed per second.
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When do catalytic converters work best?
Reactions are faster at higher temperatures, and catalytic converters work best at high temperatures.
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What do catalytic converters have that increases the rate of reaction?
Catalytic converters in cars have a high surface area to increase the rate of reaction of carbon monoxide and unburned fuel from exhaust gases with oxygen from the air to produce carbon dioxide and water.
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Why do you never get 100% of the possible yield in a chemical reaction?
You never get 100% of the possible yield because some reactants may not have reacted, the product may stick to the apparatus or otherwise get lost, or because unwanted products may be created by side reactions.
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What is theoretical yield?
The theoretical yield is the maximum amount of product that could be made if all the reactants were converted into product.
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How do you calculate the percentage yield?
actual yield / theoretical yield x 100%
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What happens to the unwanted products of a reaction?
In industry, the unwanted products of a reaction must be disposed of. This can be costly and must avoid damaging the environment or causing problems to people living nearby.
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How do economic considerations affect the chemical industry?
Economic considerations drive undustry for reactions that have a high percentage yield, make no unwanted products and occur at a suitable rate.
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What is empirical formula?
Empirical formula is the simplest ratio of atoms.
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Other cards in this set

Card 2

Front

What is an endothermic reaction?

Back

In an endothermic reaction, heat is taken in and transferred to chemical energy, so the temperature falls.

Card 3

Front

How do all chemical reactions start?

Back

Preview of the front of card 3

Card 4

Front

What happens when bonds are made?

Back

Preview of the front of card 4

Card 5

Front

Why do exothermic reactions happen?

Back

Preview of the front of card 5
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