Exothermic and Endothermic Reactions Quiz

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Questions and Answers

Which of the following are examples of exothermic reactions?

  • Neutralisation reactions (correct)
  • Thermal decomposition of calcium carbonate
  • Combustion (correct)
  • Respiration (correct)

Endothermic reactions involve the transfer of energy from the reacting chemicals to the surroundings.

False (B)

The energy change (ΔΗ) in an exothermic reaction is positive.

False (B)

In an exothermic reaction, the reactants are at a lower energy level than the products.

<p>False (B)</p> Signup and view all the answers

What is the minimum amount of energy required for a chemical reaction to take place?

<p>Activation energy</p> Signup and view all the answers

What is the name of the alternative pathway for a chemical reaction that catalysts provide?

<p>Lowering the activation energy</p> Signup and view all the answers

What is the unit used to measure bond energies?

<p>kJ/mol</p> Signup and view all the answers

Flashcards

Exothermic Reactions

Chemical reactions that release energy to the surroundings, causing the temperature to increase.

Endothermic Reactions

Chemical reactions that absorb energy from the surroundings, causing the temperature to decrease.

Reaction Profile

A visual representation of the energy changes in a chemical reaction, showing the relative energy levels of reactants and products.

Activation Energy

The minimum amount of energy required for a reaction to start.

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Catalyst

A substance that speeds up a reaction without being consumed itself, by lowering the activation energy.

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Bond Breaking

The energy change that occurs during the breaking of bonds.

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Bond Making

The energy change that occurs during the formation of bonds.

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Bond Energy

The energy required to break a specific type of bond, measured in kJ/mol.

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Calculating Energy Change

A calculation using bond energies to determine the overall energy change in a chemical reaction.

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Required Practical: Energy Changes

A practical investigation to observe temperature changes in reactions involving acid and metals, carbonates, neutralizations, and displacement reactions.

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Chemical Cell

A device that converts chemical energy into electrical energy.

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Battery

A group of chemical cells connected together in series.

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Rechargeable Cells

Chemical cells that can be recharged by reversing the chemical reactions.

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Non-rechargeable Cells

Chemical cells that cannot be recharged, they stop working when the chemicals are used up.

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Voltage

The electrical potential difference across a cell, measured in volts (V).

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Voltage and Reactivity

The voltage of a cell is determined by the difference in reactivity between the two metals used. The larger the difference in reactivity, the higher the voltage.

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Fuel Cell

A device that produces electricity continuously by supplying fuel and oxygen, without needing to be recharged.

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Hydrogen-oxygen Fuel Cell

A fuel cell that uses hydrogen and oxygen to produce electricity.

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Oxidation of Hydrogen

A chemical process that occurs in a fuel cell where hydrogen is oxidized, losing electrons.

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Reduction of Oxygen

A chemical process in a fuel cell where oxygen gains electrons.

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Redox Reaction

A chemical reaction that involves both oxidation and reduction.

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Ionic Equation

A chemical equation that shows only the ions that are involved in a reaction, omitting spectator ions.

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Spectator Ion

An ion that does not participate directly in a reaction and remains unchanged.

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Heating

The process of adding heat to a substance.

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Cooling

The process of removing heat from a substance.

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Endothermic Reaction

A reaction where heat is absorbed from the surroundings.

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Exothermic Reaction

A reaction where heat is released to the surroundings.

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Energy Level Diagram

A diagram that shows the relative energies of reactants and products in a reaction.

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Study Notes

Exothermic and Endothermic Reactions

  • Exothermic reactions release energy to the surroundings, increasing temperature. Examples include combustion, respiration, and neutralisation.
  • Endothermic reactions absorb energy from the surroundings, decreasing temperature. Examples include thermal decomposition of calcium carbonate and dissolving sherbet.

Reaction Profiles

  • Exothermic: Reactants have higher energy than products; energy is released to the surroundings.
  • Endothermic: Reactants have lower energy than products; energy is absorbed from the surroundings.

Activation Energy

  • Activation energy is the minimum energy needed for a reaction to start.
  • Catalysts lower activation energy, speeding up reactions.

Bond Making and Bond Breaking

  • Bond breaking requires energy (endothermic).
  • Bond making releases energy (exothermic).
  • Energy changes in reactions are measured in kJ/mol.

Calculations Using Bond Energies

  • Bond energies are used to calculate the overall energy change in a reaction.
  • Total bond energy of broken bonds minus total bond energy of created bonds = overall energy change.
  • Negative value indicates an exothermic reaction, positive value indicates an endothermic reaction.

Required Practical: Investigating Variables Affecting Temperature Changes

  • Aim: Investigate how different variables affect the temperature changes in reactions (e.g., acid + metal, acid + carbonate, neutralisation).
  • Equipment: Polystyrene cup, measuring cylinder, thermometer, beaker, balance.
  • Method: Control variables (acid concentration), measure starting temperature, add reactants, measure temperature change.

Chemical Cells

  • Chemical cells convert chemical energy to electrical energy.
  • Rechargeable cells can be recharged; non-rechargeable cells cannot.
  • Voltage depends on the reactivity difference between metals in the cell.

Fuel Cells

  • Fuel cells produce electricity continuously by reacting a fuel (like hydrogen) with oxygen.
  • The only product is water.
  • This process is a redox reaction, where oxidation and reduction happen simultaneously.

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