U3: Concept: 2: Chemical Reactions

Define chemical reaction:

• A process that leads to the transformation of physical substances
• A process that leads to the transformation of energy
• A process that leads to the transformation of one set of chemical substances to another

Define reactants:

• Substances present at the start of a chemical reaction
• Products formed during a chemical reaction
• Substances that are not involved in a chemical reaction
• Substances that are only present in a completed chemical reaction

Define products in a chemical reaction:

• Substances that disappear during the reaction

• The energy released during a reaction
• The starting materials in a reaction
• Substances formed as a result of the reaction

What happens to chemical bonds during chemical reactions?

• They disappear completely
• They are broken and new bonds are formed.
• They become stronger
• They remain unchanged

Energy is _​ (a)   _______ or __​ (b)   ______ whenever chemical __​ (c)   ______ are __​ (d)   ______.

• released
• absorbed
• bonds
• formed and broken
• obeyed
• raked

How do energy changes affect whether a chemical reaction will occur? Pick 2

• Chemical reactions that release energy often occur on their own, or spontaneously.

• Chemical reactions that

  absorb energy requires a source of energy.

• It makes things different in pH

• It has the ability to make or break a large number of things including what can or cannot happen to drive a bargain

How is energy released when hydrogen gas is burned?

• It reacts with carbon dioxide in the air and releases energy in the form of electricity.

• It forms a new gas and releases energy in the form of cold and darkness.
• It reacts with oxygen in the air to form water and releases energy in the form of heat and light.

• It combines with nitrogen in the air and releases energy in the form of sound and vibration.

Define activation energy:

• The energy required to stop a chemical reaction
• The maximum amount of energy required to start a chemical reaction
• Minimum amount of energy required to start a chemical reaction
• The energy released during a chemical reaction

Looking at Figure 2-22, how does the energy of the reactants and products differ between an energy-absorbing reaction and an energy-releasing reaction?

Answer explanation

14. In the energy absorbing reaction, the energy of the reactants is lower than that of the products. Conversely, in

an energy-releasing reaction, the energy of the reactants is higher than that of the products.

What is a catalyst:

• A substance that has no effect on the rate of a chemical reaction
• A substance that decreases the rate of a chemical reaction
• A substance that undergoes permanent change during a chemical reaction
• A substance that increases the rate of a chemical reaction without undergoing any permanent change itself.