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4 years ago

A chemical reaction gives off 1,500 kj of heat energy. about how many calories is this? (1 calorie = 4.18 joules)

Chemistry

2 answers:

Greeley [361]4 years ago

6 0

1500kj = 15x 10^5 j
1 calorie = 4.18 j
(15 x 10^5)/4.18= 3.58 x 10^5

Answer is a

Zanzabum4 years ago

3 0

Answer is: a. 3.6 x 10^5 calories.

E = 1500 kJ; heat energy.

E = 1500 kJ · 1000 J/kJ.

E = 1500000 J = 1.5·10⁶ J.

E = 1.5·10⁶ J ÷ 4.18 J/cal.

E = 3.6·10⁵ cal.

Calorie (cal), or small calorie, is the amount of energy needed to heat one gram of water by one degree Celsius.

One small calorie is approximately 4.18 joules.

A calorie is a unit of energy.

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If acetic acid is the only acid that vinegar contains (ka=1.8×10−5), calculate the concentration of acetic acid in the vinegar.

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$CH_{3}COOH \ \textless \ ---\ \textgreater \ H^{+} + CH_{3}COO^{-}$

In this case pH value of the solution is necessary to calculate the concentration but it's not given here so pH = 2.88 (looked it up)

pH = 2.88 ==> $[H^{+}]$ = $10^{-2.88}$ = 0.001 $moldm^{-3}$

The change in Concentration Δ $[CH_{3}COOH]$ = 0.001 $moldm^{-3}$

  CH3COOH H+ CH3COOH
Initial   $moldm^{-3}$      $x$ 0 0

Change $moldm^{-3}$ -0.001 +0.001 +0.001

Equilibrium $moldm^{-3}$ $x$ - 0.001 0.001 0.001


Since the $k_{a}$ value is so small, the assumption
$[CH_{3}COOH]_{initial} = [CH_{3}COOH]_{equilibrium}$ can be made.

$k_{a} = [tex]= 1.8*10^{-5} = \frac{[H^{+}][CH_{3}COO^{-}]}{[CH_{3}COOH]} = \frac{0.001^{2}}{x}$

Solve for x to get the required concentration.

note: 1.)Since you need the answer in 2SF don&t round up values in the middle of the calculation like I've done here.

2.) The ICE (Initial, Change, Equilibrium) table may come in handy if you are new to problems of this kind

Hope this helps!

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Explanation:

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f = V/λ ........................... (1)

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