Chemistry

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1. The delta Hf of an element in its standard state is defined to be
a) 0 kJ/mol
b) 10 kJ/mol
c) -10 kJ/mol
d) greater than 0 kJ/mol
e) a unique value for each element

I am assuming its a?

2. Which of the following statements are true?
I) The reaction vessel cools when an endothermic reaction occurs.
II)An endothermic reaction has a negative value of delta H.
III)Heat is liberated when an exothermic reaction occurs.

a) I and II
b) I, II, and III
c) I and III only
d) II and III only
e) none of them

I am thinking that it's d?

3. Which factor does not affect the rate of a chemical reaction in aqueous solution?

a) The enthalpy change of the reaction
b) The activation energy of the reaction
c) The collision frequency of the reaction particles
d) The relative orientation of the colliding particles
e) The temperature of the solution.

It's a?

4. Which of the following processes are exothermic?
I) Boiling water
II) Freezing water
III) Condensing steam
IV) Melting ice

a) I and II only
b) II and III only
c) I and IV only
d) II, III, and IV only
e) II and IV only

it's b?

5. Which statement about an activate complex is true?
a) It is a stable substance
b) It has lower chemical potential energy, or enthalpy, than reactants or products.
c) It occurs only in endothermic reactions
d) It occurs at the transition state of the reaction
e) It always breaks down to form product molecules.

I am assuming it's d?

6. A catalyst changes the
I) Mechanism of a reaction
II) Enthalpy change of a reaction
III) Activation energy of a reaction

a) I only
b) III only
c) I and III only
d) II and III only
e) I, II, and III

I think it's b

  • Chemistry -

    1. The delta Hf of an element in its standard state is defined to be
    a) 0 kJ/mol
    b) 10 kJ/mol
    c) -10 kJ/mol
    d) greater than 0 kJ/mol
    e) a unique value for each element

    I am assuming its a?
    You should be SURE it's a.

    2. Which of the following statements are true?
    I) The reaction vessel cools when an endothermic reaction occurs.
    II)An endothermic reaction has a negative value of delta H.
    III)Heat is liberated when an exothermic reaction occurs.

    a) I and II
    b) I, II, and III
    c) I and III only
    d) II and III only
    e) none of them

    I am thinking that it's d?
    No. Exothermic means heat is given off. Endothermic means heat is absorbed. d isn't correct. III is correct. II can't be correct. By definition exothermic reactions have - delta H and endothermic is + delta H. So the only other choice is I and that is correct, also. When the reaction absorbs heat it must take it from somewhere. The most obvious choice is from it's surroundings and that's the reaction container. So the container gets cold.


    3. Which factor does not affect the rate of a chemical reaction in aqueous solution?

    a) The enthalpy change of the reaction
    b) The activation energy of the reaction
    c) The collision frequency of the reaction particles
    d) The relative orientation of the colliding particles
    e) The temperature of the solution.

    It's a?yes

    4. Which of the following processes are exothermic?
    I) Boiling water
    II) Freezing water
    III) Condensing steam
    IV) Melting ice

    a) I and II only
    b) II and III only
    c) I and IV only
    d) II, III, and IV only
    e) II and IV only

    it's b?yes

    5. Which statement about an activate complex is true?
    a) It is a stable substance
    b) It has lower chemical potential energy, or enthalpy, than reactants or products.
    c) It occurs only in endothermic reactions
    d) It occurs at the transition state of the reaction
    e) It always breaks down to form product molecules.

    I am assuming it's d?I would go with d

    6. A catalyst changes the
    I) Mechanism of a reaction
    II) Enthalpy change of a reaction
    III) Activation energy of a reaction

    a) I only
    b) III only
    c) I and III only
    d) II and III only
    e) I, II, and III

    I think it's b I don't know about this since the directions are not clear. III is correct but since the word only appears I assume more than one of the answers can be correct. I would argue that a catalyst could change the mechanism of the reaction by allowing the reactants to form an "intermediate complex."

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