1. How do endothermic and exothermic reactions differ?
a. Endothermic reactions release energy and are spontaneous.
b. Exothermic reactions release energy and are spontaneous.
c. Endothermic reactions give off heat and light.
d. Photosynthesis is exothermic.
MY CHOICE: B
2. Which is NOT a description of activation energy?
a. The energy absorbed by the reactants.
b. The energy needed to get an endothermic reaction to proceed.
c. The "push" to start a chemical reaction.
d. The energy transfer between the products and reactants.
MY CHOICE: D
3. An animal's stomach contains enzymes that break down food into smaller molecules that the animal's cells can use. Enzymes perform this function by:
a. participating in chemical reactions
b. increasing the temperature
c. changing the ionic concentration
d. lowering the pH
MY CHOICE: A
4. Milk you buy at the store has been “Pasteurized.” This means the milk was warmed up to around 150 F/65 C to kill harmful bacteria. This process probably works because:
a. it speeds up the metabolism of the bacteria and this increases their death rate
b. it causes the bacteria’s carbohydrates to under go hydrolysis, thus killing the bacteria
c. the bacteria’s enzymes will denature at the high temperature, thus killing the bacteria
d. it causes the bacteria to build many polymers, which kills the bacteria
MY CHOICE: C
5. In a test tube, a student used the enzyme catalase to break down some H2O2 (Hydrogen Peroxide). After the reaction, she discovered another bottle of H2O2 that needed to be broken down also. Will she be able to use the enzyme again?
a. No, because enzymes get broken down when they do chemical reactions
b. Yes, because enzymes are carbohydrates and does not break them down
c. No, because the enzymes denature after doing chemical reactions
d. Yes, because enzymes are not used up by the reactions they help speed up
MY CHOICE: D
Your choices are correct!
1. B - Exothermic reactions release energy and are spontaneous.
2. D - The energy transfer between the products and reactants.
3. A - Enzymes participate in chemical reactions.
4. C - The bacteria's enzymes will denature at the high temperature, thus killing the bacteria.
5. D - Yes, because enzymes are not used up by the reactions they help speed up.
1. The correct answer is b. Exothermic reactions release energy and are spontaneous. Endothermic reactions absorb energy and are not spontaneous.
2. The correct answer is d. The energy transfer between the products and reactants is not a description of activation energy. Activation energy refers to the energy needed to start a chemical reaction.
3. The correct answer is a. Enzymes participate in chemical reactions by facilitating the conversion of substrates into products.
4. The correct answer is c. Pasteurization works because the high temperature denatures the bacteria's enzymes, leading to their death.
5. The correct answer is d. Enzymes are not used up by the reactions they help speed up, so the student will be able to use the enzyme catalase again.
1. The correct answer is B. Exothermic reactions release energy and are spontaneous. Endothermic reactions, on the other hand, absorb energy from the surroundings and are non-spontaneous.
To understand this, you can think of energy as a currency in chemical reactions. In exothermic reactions, the reactants have more potential energy stored in their chemical bonds compared to the products. This excess energy is released into the surroundings as heat or light, resulting in a decrease in the overall energy of the system. These reactions are spontaneous because they release energy and can occur on their own without external intervention.
In contrast, endothermic reactions require an input of energy from the surroundings to proceed. The reactants have lower potential energy than the products, so energy must be absorbed for the reaction to occur. This absorption of energy often occurs in the form of heat, making the surroundings cooler. Endothermic reactions are non-spontaneous because they require energy input and do not occur naturally without external intervention.
2. The correct answer is D. Activation energy is not the energy transfer between the products and reactants.
Activation energy is the minimum amount of energy required to initiate a chemical reaction. It can be thought of as the "push" needed to start the reaction. Even if a reaction is exothermic or endothermic, it still requires activation energy to proceed. This energy is used to break the existing chemical bonds in the reactants, allowing new bonds to form in the products.
3. The correct answer is A. Enzymes perform their function by participating in chemical reactions.
Enzymes are specialized proteins that act as catalysts in living organisms. They speed up chemical reactions by lowering the activation energy required for the reaction to occur. Enzymes achieve this by temporarily binding to the reactant molecules, forming an enzyme-substrate complex. This complex allows the reactants to come together in the correct orientation, making it easier for the reaction to proceed.
4. The correct answer is C. The bacteria's enzymes will denature at the high temperature, thus killing the bacteria.
Pasteurization is a process used to kill harmful bacteria in food products, such as milk. By heating the milk to a specific temperature and holding it there for a certain period of time, the bacteria present in the milk are killed. The high temperature causes the enzymes in the bacteria to denature, meaning their 3D structure is disrupted. This leads to a loss of enzymatic activity and functionality, ultimately resulting in the death of the bacteria.
5. The correct answer is D. Enzymes are not used up by the reactions they help speed up.
Enzymes are catalysts, which means they speed up chemical reactions without being consumed or changed themselves. In the case of catalase, it helps break down hydrogen peroxide into water and oxygen. After the reaction, the enzyme remains unchanged and can be used again to catalyze the breakdown of another molecule of hydrogen peroxide. This ability of enzymes to be reused makes them highly efficient and important in biological systems.